chore: make OSS Docker image build manual-only (#10190)

## Summary
- Switch `build-pr-image.yml` from auto-triggering on every PR to
`workflow_dispatch` only

## Why
OSS Docker image builds on every PR waste CI compute. The image isn't
always needed — developers can trigger it manually when required.

---------

Co-authored-by: Yashodhan Joshi <yashodhan@openobserve.ai>

.github/workflows/build-pr-image.yml

@@ -1,56 +1,26 @@
 name: Build PR Docker Image
 
 on:
-  pull_request:
-    branches:
-      - "*"
+  workflow_dispatch:
+    inputs:
+      branch:
+        description: 'Branch to build (e.g., feature/my-branch)'
+        required: true
+        type: string
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  group: ${{ github.workflow }}-${{ inputs.branch }}
   cancel-in-progress: true
 
 env:
   AWS_REGION: us-east-1
 
 jobs:
-  check_changes:
-    runs-on: ubuntu-latest
-    permissions:
-      contents: read
-    outputs:
-      has_changes: ${{ steps.check_changes.outputs.has_changes }}
-      should_build: ${{ steps.check_changes.outputs.should_build }}
-    steps:
-      - name: Clone the current repo
-        uses: actions/checkout@v5
-        with:
-          fetch-depth: 0
-
-      - name: Check if relevant code has changes
-        id: check_changes
-        run: |
-          if git diff --name-only origin/${{ github.base_ref || 'main' }} ${{ github.sha }} | grep -qvE '\.(md|yml|yaml)$'; then
-            echo "has_changes=true" >> $GITHUB_OUTPUT
-          else
-            echo "has_changes=false" >> $GITHUB_OUTPUT
-          fi
-
-          # Also check if this is a non-fork PR
-          if [ "${{ github.event_name }}" == "pull_request" ] && \
-             [ "${{ github.event.pull_request.head.repo.full_name }}" == "${{ github.repository }}" ] && \
-             [ "${{ github.event.pull_request.head.repo.fork }}" == "false" ]; then
-            echo "should_build=true" >> $GITHUB_OUTPUT
-          else
-            echo "should_build=false" >> $GITHUB_OUTPUT
-          fi
-
   build_pr_image_amd64:
     name: build_pr_image_amd64
-    needs: check_changes
     permissions:
       id-token: write
       contents: read
-    if: needs.check_changes.outputs.has_changes == 'true' && needs.check_changes.outputs.should_build == 'true'
     runs-on: ubicloud-standard-8
     steps:
       - name: Remove unused tools
@@ -63,8 +33,8 @@ jobs:
       - name: Clone the current repo
         uses: actions/checkout@v5
         with:
-          repository: ${{ github.event.pull_request.head.repo.full_name }}
-          ref: ${{ github.event.pull_request.head.ref || github.ref }}
+          repository: ${{ github.repository }}
+          ref: ${{ inputs.branch }}
           fetch-depth: 0
           fetch-tags: true
 
@@ -133,11 +103,9 @@ jobs:
 
   build_pr_image_arm64:
     name: build_pr_image_arm64
-    needs: check_changes
     permissions:
       id-token: write
       contents: read
-    if: needs.check_changes.outputs.has_changes == 'true' && needs.check_changes.outputs.should_build == 'true'
     runs-on: "ubicloud-standard-16-arm"
     steps:
       - name: Remove unused tools
@@ -150,8 +118,8 @@ jobs:
       - name: Clone the current repo
         uses: actions/checkout@v5
         with:
-          repository: ${{ github.event.pull_request.head.repo.full_name }}
-          ref: ${{ github.event.pull_request.head.ref || github.ref }}
+          repository: ${{ github.repository }}
+          ref: ${{ inputs.branch }}
           fetch-depth: 0
           fetch-tags: true
 
@@ -229,8 +197,8 @@ jobs:
       - name: Clone the current repo
         uses: actions/checkout@v5
         with:
-          repository: ${{ github.event.pull_request.head.repo.full_name }}
-          ref: ${{ github.event.pull_request.head.ref || github.ref }}
+          repository: ${{ github.repository }}
+          ref: ${{ inputs.branch }}
           fetch-depth: 0
           fetch-tags: true
       - name: Set GIT_TAG env
@@ -261,16 +229,11 @@ jobs:
   build_pr_image_summary:
     runs-on: ubuntu-latest
     permissions: {}
-    needs: [check_changes, build_pr_image_amd64, build_pr_image_arm64, build]
+    needs: [build_pr_image_amd64, build_pr_image_arm64, build]
     if: always()
     steps:
       - name: Check build results
         run: |
-          if [ "${{ needs.check_changes.outputs.has_changes }}" != "true" ] || [ "${{ needs.check_changes.outputs.should_build }}" != "true" ]; then
-            echo "No relevant changes or not a non-fork PR - builds skipped"
-            exit 0
-          fi
-
           if [ "${{ needs.build_pr_image_amd64.result }}" == "success" ] || [ "${{ needs.build_pr_image_amd64.result }}" == "skipped" ]; then
             echo "AMD64 build passed or skipped"
           else