[Requires repository secret addition] Add Publish to Buf Github Action (#508)

_**READ BEFORE MERGING:** All PRs require approval by both Server AND
SDK teams before merging! This is why the number of required approvals
is "2" and not "1"--two reviewers from the same team is NOT sufficient.
If your PR is not approved by someone in BOTH teams, it may be summarily
reverted._

<!-- Describe what has changed in this PR -->
**What changed?**
Adds a GitHub Actions workflow to automate the process of pushing
protocol buffers to the Buf registry on every push to the main branch.

We need to set the `BUF_TOKEN` secret before merging this PR.

<!-- Tell your future self why have you made these changes -->
**Why?**
We want to be able to depend on server protos from other repositories
(e.g. api-cloud) using the buf package manager.


<!-- Are there any breaking changes on binary or code level? -->
**Breaking changes**
None.

<!-- If this breaks the Server, please provide the Server PR to merge
right after this PR was merged. -->
**Server PR**
NA

Author: nikki-dag

.github/workflows/push-to-buf.yml

@@ -0,0 +1,20 @@
+name: Push to Buf Registry
+
+on:
+  push:
+    tags:
+      - 'v**'
+    branches:
+      - master
+permissions:
+  contents: read
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+      - uses: bufbuild/buf-action@v1
+        with:
+          version: 1.49.0
+          token: ${{ secrets.BUF_TEMPORALIO_TOKEN }}

buf.yaml

@@ -1,4 +1,5 @@
 version: v1
+name: buf.build/temporalio/api
 deps:
   - buf.build/grpc-ecosystem/grpc-gateway
   - buf.build/googleapis/googleapis