ci: Add auto-label GH action (#5163)

### Description
Add a GH action that auto-labels PRs based on title.

If a PR is opened or edited, the action:
- reads the existing labels
- if there already is a Changelog label, it terminates early to not
overwrite whatever the developer chose
- if there is no Changelog label, it reads the PR title and matches it
against a map of common patterns
- if it matches, the label is added
- if there is no match, it doesn't add a label

#### Issues
<!--
* resolves: #1234
* resolves: LIN-1234
-->

#### Reminders
- Please add tests to validate your changes, and lint your code using
`tox -e linters`.
- Add GH Issue ID _&_ Linear ID (if applicable)
- PR title should use [conventional
commit](https://develop.sentry.dev/engineering-practices/commit-messages/#type)
style (`feat:`, `fix:`, `ref:`, `meta:`)
- For external contributors:
[CONTRIBUTING.md](https://github.com/getsentry/sentry-python/blob/master/CONTRIBUTING.md),
[Sentry SDK development docs](https://develop.sentry.dev/sdk/), [Discord
community](https://discord.gg/Ww9hbqr)

Author: sentrivana

.github/release.yml

@@ -1,3 +1,8 @@
+# This configuration is used by Craft to categorize changelog entries based on
+# PR labels. To avoid some manual work, there is a PR labeling GitHub action in
+# .github/workflows/pr-labeler.yml that adds a changelog label to PRs based on
+# the title.
+
 changelog:
   exclude:
     labels:

.github/workflows/pr-labeler.yml

@@ -0,0 +1,72 @@
+# This action adds changelog labels to PRs that are then used by the release
+# notes generator in Craft. The configuration for which labels map to what
+# changelog categories can be found in .github/release.yml.
+
+name: Label PR for Changelog
+
+on:
+  pull_request:
+    types: [opened, edited]
+
+permissions:
+  pull-requests: write
+
+jobs:
+  label:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Add changelog label
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const title = context.payload.pull_request.title.toLowerCase();
+            const prNumber = context.payload.pull_request.number;
+
+            // Get current labels
+            const { data: currentLabels } = await github.rest.issues.listLabelsOnIssue({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: prNumber,
+            });
+
+            // Check if a Changelog label already exists
+            const hasChangelogLabel = currentLabels.some(label =>
+              label.name.startsWith('Changelog:') || label.name === 'skip-changelog'
+            );
+
+            if (hasChangelogLabel) {
+              console.log('PR already has a Changelog label, skipping');
+              return;
+            }
+
+            // Determine which label to apply
+            let newLabel = null;
+
+            if (title.includes('deprecate')) {
+              newLabel = 'Changelog: Deprecation';
+            } else if (title.startsWith('feat')) {
+              newLabel = 'Changelog: Feature';
+            } else if (title.startsWith('fix') || title.startsWith('bugfix')) {
+              newLabel = 'Changelog: Bugfix';
+            } else if (title.startsWith('docs')) {
+              newLabel = 'Changelog: Docs';
+            } else if (title.startsWith('ref') || title.startsWith('test')) {
+              newLabel = 'Changelog: Internal';
+            } else if (title.startsWith('ci') || title.startsWith('build')) {
+              newLabel = 'skip-changelog';
+            }
+
+            // Apply the new label if one was determined
+            if (newLabel) {
+              await github.rest.issues.addLabels({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: prNumber,
+                labels: [newLabel],
+              });
+
+              console.log(`Applied label: ${newLabel}`);
+            } else {
+              console.log('No matching label pattern found in PR title, please add manually');
+            }
+