gh-37262: Added automatic size labeler

    
I have implemented the `automatic size labeler`, which now assigns
labels to pull requests based on the number of lines changed

**Minimal**
Typically involves very small changes, bug fixes, or updates that
require only a few lines of code, often less than 50.
#37208 #37146 #37043

**Small**
Involves more substantial changes than minimal, potentially adding new
features or making modifications to existing ones. The range is usually
between 50 to 100 lines of code.
#37152 #37132

**Moderate**
Represents a significant portion of the codebase being modified, such as
adding new features, refactoring, or making extensive changes to
existing functionalities. This might involve between 100 to 300 lines of
code.
#36919 #37112

**Large**
Involves substantial and complex changes across various parts of the
codebase. This could include major architectural changes, the
introduction of new modules, or a significant overhaul of existing
features, often exceeding 300 lines of code.
#37125 #36977 #36972

### 📝 Checklist

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Fixes: #37254
    
URL: #37262
Reported by: Aman Moon
Reviewer(s): Sebastian Oehms

.github/workflows/pr-labeler.yml

@@ -0,0 +1,39 @@
+# This action automatically labels Pull-Requests
+# based on files edited and no of lines changed.
+name: Size Labeler/Checker
+on:
+  pull_request_target:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - ready_for_review
+      - review_requested
+      - edited
+jobs:
+  label-changes:
+    if: vars.SMALL_THRESHOLD && vars.MODERATE_THRESHOLD && vars.LARGE_THRESHOLD && github.event.pull_request.draft == false
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+
+      - name: Add labels based on size
+        run: |
+          git fetch origin $BASE_SHA
+          chmod a+x .github/workflows/set_labels_by_changes.sh
+          .github/workflows/set_labels_by_changes.sh
+        env:
+          BASE_SHA: ${{ github.base_ref }}
+          PR_BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          PR_HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          REPOSITORY: ${{ github.repository }}
+          PR_NUMBER: ${{ github.event.pull_request.number}}
+          SMALL_THRESHOLD: ${{ vars.SMALL_THRESHOLD }}
+          MODERATE_THRESHOLD: ${{ vars.MODERATE_THRESHOLD }}
+          LARGE_THRESHOLD: ${{ vars.LARGE_THRESHOLD }}

.github/workflows/set_labels_by_changes.sh

@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+
+echo 'set_labels_by_changes.sh called with environment:'
+echo "BASE SHA: $PR_BASE_SHA" 
+echo "HEAD SHA: $PR_HEAD_SHA" 
+echo "SMALL THRESHOLD $SMALL_THRESHOLD"
+echo "MODERATE THERESHOLD: $MODERATE_THRESHOLD"
+echo "LARGE THRESHOLD: $LARGE_THRESHOLD"
+
+# get all the changes made and changed files
+CHANGES=$(git diff --ignore-all-space $PR_BASE_SHA $PR_HEAD_SHA)
+
+# ignore blank lines
+CHANGES=$(echo "$CHANGES" | grep -vE '^[\+\-]\s*$')
+
+# ignore non necessary lines from git diff
+CHANGES=$(echo "$CHANGES" | grep -E '^[+\-]' | grep -vE '^\+\+\+|^\-\-\-')
+
+# count total no of lines
+CHANGES=$(echo "$CHANGES" | wc -l)
+
+echo "CHANGES MADE: $CHANGES"
+
+AUTH_HEADER="Authorization: Bearer $GITHUB_TOKEN"
+
+MINIMAL="v: minimal"
+SMALL="v: small"
+MODERATE="v: moderate"
+LARGE="v: large"
+
+DELETE_LABELS=("$MINIMAL" "$SMALL" "$MODERATE" "$LARGE")
+
+if [ "$CHANGES" -gt "$LARGE_THRESHOLD" ]; then
+    SIZE_LABEL="$LARGE"
+elif [ "$CHANGES" -gt "$MODERATE_THRESHOLD" ]; then
+    SIZE_LABEL="$MODERATE"
+elif [ "$CHANGES" -gt "$SMALL_THRESHOLD" ]; then
+    SIZE_LABEL="$SMALL"
+else
+    SIZE_LABEL="$MINIMAL"
+fi
+
+DELETE_LABELS=("${DELETE_LABELS[@]//${SIZE_LABEL}/}")
+
+# API for adding labels on the Pull Request 
+API_URL="https://api.github.com/repos/$REPOSITORY/issues/$PR_NUMBER/labels"
+
+echo "Adding label: ${SIZE_LABEL[@]}"
+for LABEL in "${SIZE_LABEL[@]}"; do
+    curl -X POST \
+        -H "$AUTH_HEADER" \
+        -H "Accept: application/vnd.github+json" \
+        -H "X-GitHub-Api-Version: 2022-11-28" \
+        -d "{\"labels\":[\"$LABEL\"]}" \
+        "$API_URL" >/dev/null
+done
+
+echo "Deleting Labels:"
+
+for DELETE_LABEL in "${DELETE_LABELS[@]}"; do
+    ENCODED_LABEL=$(echo "$DELETE_LABEL" | sed 's/ /%20/g')
+    curl -X DELETE \
+        -H "Accept: application/vnd.github+json" \
+        -H "$AUTH_HEADER" \
+        -H "X-GitHub-Api-Version: 2022-11-28" \
+        "$API_URL/$ENCODED_LABEL" >/dev/null
+done