Add a script for running through some basic repository setup

[roypat]

Summary of the PR

Add a repository_setup.sh script that automates a couple of setup steps
for setup of new rust-vmm repositories. It also supports updating the
configuration of already created repositories by comparing the
repository's configuration to the defaults in rust-vmm-ci and giving the
option to update.

Currently, the script supports dependabot setup and .platform file
generation. It does not deal with the coverage files, since I am still
hoping to switch us over to codecov.io in the future, at which point
that will all changes completely anyway. I plan to also add crates.io
publish workflow support before moving this out of draft.

Requirements

Before submitting your PR, please make sure you addressed the following
requirements:

• All commits in this PR have Signed-Off-By trailers (with
  git commit -s), and the commit message has max 60 characters for the
  summary and max 75 characters for each description line.
• All added/changed functionality has a corresponding unit/integration
  test.
• All added/changed public-facing functionality has entries in the "Upcoming
  Release" section of CHANGELOG.md (if no such section exists, please create one).
• Any newly added unsafe code is properly documented.

[roypat]

Sample output of running this script in the vhost repository:

$ ./rust-vmm-ci/repository_setup.sh 
Welcome to the rust-vmm interactive repository setup!

This script will guide you through initializing basic components of a fresh
rust-vmm repository, or alternatively lets you update the configuration of an
existing repository (for example, if since the first setup of a repository,
rust-vmm-ci has added new features that you would like to use).

Please select the hardware plaforms for which you would like to enable CI support:
Enable support for x86_64? [Y/n] y
Enable support for aarch64? [Y/n] y
Enable support for riscv64? [Y/n] n

Dependabot is already configured, although configuration does not match any rust-vmm-ci provided ones. Would you like to reconfigure dependabot? [Y/n] y
Dependabot allow you to automatically receive PRs for bumping your cargo
dependencies, as well as for updating the rust-vmm-ci submodule. You can choose
to run dependabot on different schedules: weekly monthly.

Which schedule would you like to enable? (say 'n' to disable dependabot)
1) weekly
2) monthly
#? 1
Configured for weekly schedule

Setting up auto-publish for crates.io upon creation of GitHub tags...
Found workspace member 'vhost' at 'vhost'. Setup auto-publish? [Y/n] y
If not already done, go to https://crates.io/crates/vhost/settings and add publish-vhost.yml as a trusted publisher!
Found workspace member 'vhost-user-backend' at 'vhost-user-backend'. Setup auto-publish? [Y/n] y
If not already done, go to https://crates.io/crates/vhost-user-backend/settings and add publish-vhost-user-backend.yml as a trusted publisher!

where the following changes would be made:

diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 37675b73db2b..973292a9c3bc 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -1,18 +1,27 @@
 version: 2
 updates:
-- package-ecosystem: cargo
+
+# A weekly update of the rust-vmm-ci submodule
+- package-ecosystem: gitsubmodule
   directory: "/"
   schedule:
     interval: weekly
-  allow:
-  - dependency-type: direct
-  - dependency-type: indirect
-  groups:
-      vhost:
-        patterns:
-          - "*"
-- package-ecosystem: gitsubmodule
+    day: monday
+  open-pull-requests-limit: 1
+
+# A weekly update to rust dependencies. These will be grouped,
+# e.g. one PR will contains updates for all dependencies.
+- package-ecosystem: cargo
   directory: "/"
   schedule:
     interval: weekly
-  open-pull-requests-limit: 10
+    day: monday
+  open-pull-requests-limit: 1
+  # Make it also update transitive dependencies in Cargo.lock
+  allow:
+    - dependency-type: "all"
+  # Group all available updates into a group called "rust-dependencies"
+  groups:
+    rust-dependencies:
+      patterns:
+        - "*"
diff --git a/.github/workflows/publish-vhost-user-backend.yml b/.github/workflows/publish-vhost-user-backend.yml
new file mode 100644
index 000000000000..24aa8ed12116
--- /dev/null
+++ b/.github/workflows/publish-vhost-user-backend.yml
@@ -0,0 +1,21 @@
+name: Publish to crates.io
+
+on:
+  push:
+    tags: ['vhost-user-backend-v*']  # Triggers when pushing version tags
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    # environment: release  # Optional: for enhanced security
+    permissions:
+      id-token: write     # Required for OIDC token exchange
+    steps:
+    - uses: actions/checkout@v4
+    - uses: rust-lang/crates-io-auth-action@v1
+      id: auth
+    - run: |
+        cd vhost-user-backend
+        cargo publish
+      env:
+        CARGO_REGISTRY_TOKEN: ${{ steps.auth.outputs.token }}
\ No newline at end of file
diff --git a/.github/workflows/publish-vhost.yml b/.github/workflows/publish-vhost.yml
new file mode 100644
index 000000000000..5bbba7cf6a64
--- /dev/null
+++ b/.github/workflows/publish-vhost.yml
@@ -0,0 +1,21 @@
+name: Publish to crates.io
+
+on:
+  push:
+    tags: ['vhost-v*']  # Triggers when pushing version tags
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    # environment: release  # Optional: for enhanced security
+    permissions:
+      id-token: write     # Required for OIDC token exchange
+    steps:
+    - uses: actions/checkout@v4
+    - uses: rust-lang/crates-io-auth-action@v1
+      id: auth
+    - run: |
+        cd vhost
+        cargo publish
+      env:
+        CARGO_REGISTRY_TOKEN: ${{ steps.auth.outputs.token }}
\ No newline at end of file
diff --git a/.platform b/.platform
new file mode 100644
index 000000000000..86353074a1f4
--- /dev/null
+++ b/.platform
@@ -0,0 +1,2 @@
+x86_64
+aarch64

[roypat]

And running it a second time on the vhost repo produces

./rust-vmm-ci/repository_setup.sh 
Welcome to the rust-vmm interactive repository setup!

This script will guide you through initializing basic components of a fresh
rust-vmm repository, or alternatively lets you update the configuration of an
existing repository (for example, if since the first setup of a repository,
rust-vmm-ci has added new features that you would like to use).

This repository already has a .platform file setup. Do you want to regenerate it? Current supported platforms are: x86_64 aarch64  [Y/n] n

Dependabot is already setup for the weekly schedule. Would you like to reconfigure dependabot? [Y/n] n

Setting up auto-publish for crates.io upon creation of GitHub tags...
Publish workflow for vhost already setup, skipping
Publish workflow for vhost-user-backend already setup, skipping

and no further changes