sagemathgh-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.
sagemath#37208 sagemath#37146 sagemath#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.
sagemath#37152 sagemath#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.
sagemath#36919 sagemath#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.
sagemath#37125 sagemath#36977 sagemath#36972

### 📝 Checklist

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Fixes: sagemath#37254
    
URL: sagemath#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