Add RELEASE.md and tag.yaml

Author: tnthornton

.github/workflows/tag.yaml

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+name: Tag
+
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'Release version (e.g. v0.1.0)'
+        required: true
+      message:
+        description: 'Tag message'
+        required: true
+
+jobs:
+  create-tag:
+    runs-on: blacksmith-2vcpu-ubuntu-2404
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Create Tag
+        uses: negz/create-tag@39bae1e0932567a58c20dea5a1a0d18358503320 # v1
+        with:
+          version: ${{ github.event.inputs.version }}
+          message: ${{ github.event.inputs.message }}
+          token: ${{ secrets.GITHUB_TOKEN }}

RELEASE.md

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+## Release Process
+
+This is a slimmed-down version of the release process described [here](https://github.com/crossplane/release).
+
+1. **feature freeze**: Merge all completed features into main development branch
+   of all repos to begin "feature freeze" period.
+1. **branch repo**: Create a new release branch using the GitHub UI for the
+   repo (e.g. `release-0.25`).
+1. **tag release**: Run the `Tag` action on the _release branch_ with the
+   desired version (e.g. `v0.25.0`).
+1. **build/publish**: Run the `CI` action on the tag.
+1. **tag next pre-release**: Run the `tag` action on the main development branch
+   with the `-0.rc.0` for the next release (e.g. `v0.26.0-0.rc.0`). (**NOTE**:
+   we added the `-0.` prefix to allow correctly sorting release candidates)
+1. **verify**: Verify all artifacts have been published successfully, perform
+   sanity testing.
+   - Check in Upbound Marketplace that the new versions are present.
+1. **release notes**:
+   - Open the new release tag in https://github.com/upbound/marketplace-mcp-server/tags and click "Create
+     release from tag".
+   - "Generate release notes" from previous release ("auto" might not work).
+   - Make sure the release notes are complete, presize and well formatted.
+   - Publish the well authored Github release.
+1. **announce**: Announce the release on Twitter, Slack, etc.
+   - Crossplane Slack #Upbound: https://crossplane.slack.com/archives/C01TRKD4623
+   - TODO: where else?