Add workflow for CLI releases (#160)

This adds a manual workflow for the CLI release process
to update `bufbuild/buf` to the version being released.

.github/workflows/update-buf-version.yaml

@@ -0,0 +1,39 @@
+name: Update bufbuild/buf Version
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        type: string
+        description: The version you intend to release (e.g. x.y.z)
+        required: true
+permissions:
+  contents: write
+  pull-requests: write
+env:
+  RELEASE_BUF_VERSION: ${{ github.event.inputs.version }}
+
+jobs:
+  prepare:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Validate input version
+        if: ${{ startsWith(github.event.inputs.version, 'v') }}
+        run: |
+          echo "error: version must not start with 'v'."
+          exit 1
+      - name: Checkout repository code
+        uses: actions/checkout@v4
+        with:
+          token: ${{ steps.app_token.outputs.token }}
+      - name: Update Buf Version
+        run: make updatebufversion
+      - name: Create PR
+        run: |
+          git config user.name "${{ github.actor }}"
+          git config user.email "${{ github.actor }}@users.noreply.github.com"
+          BRANCH="release/v${RELEASE_BUF_VERSION}"
+          git switch -C ${BRANCH}
+          git add make/go/dep_buf.mk
+          git commit -m "Update version to ${RELEASE_BUF_VERSION}"
+          git push --set-upstream origin --force ${BRANCH} 
+          gh pr create --title "Update buf version to v${RELEASE_BUF_VERSION}" --body "Update buf version to newly released version, ${RELEASE_BUF_VERSION}."

make/go/buf.mk

@@ -62,3 +62,8 @@ bufbreaking: $(BUF)
 postlint:: bufbreaking
 endif
 endif
+
+.PHONY: updatebufversion
+updatebufversion:
+	$(SED_I) -E "s/BUF_VERSION \?=.*/BUF_VERSION ?= ${RELEASE_BUF_VERSION}/" "make/go/dep_buf.mk"
+	$(SED_I) -E "s/\# https\:\/\/github.com\/bufbuild\/buf\/releases.*/\# https\:\/\/github.com\/bufbuild\/buf\/releases $(shell date "+%Y%m%d") checked $(shell date "+%Y%m%d")/" "make/go/dep_buf.mk"