Generate release notes from PR labels (#265)

This change enables automatic release notes from labels. It also
enforces a changelog label for all PRs.

Categorizing changes will make it easier for users to understand what
changed in each release.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

## Chores
* Implemented automated changelog categorization and pull request label
enforcement to organize release notes into semantic sections (Added,
Changed, Fixed, Deprecated, Removed, Security, Dependencies) for
improved clarity in future releases.

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[![Review Change
Stack](https://storage.googleapis.com/coderabbit_public_assets/review-stack-in-coderabbit-ui.svg)](https://app.coderabbit.ai/change-stack/netbirdio/kubernetes-operator/pull/265?utm_source=github_walkthrough&utm_medium=github&utm_campaign=change_stack)

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<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Signed-off-by: Philip Laine <philip.laine@gmail.com>

.github/release.yaml

@@ -0,0 +1,25 @@
+changelog:
+  exclude-labels:
+    - changelog/ignore
+  categories:
+    - title: Added
+      labels:
+        - changelog/added
+    - title: Changed
+      labels:
+        - changelog/changed
+    - title: Fixed
+      labels:
+        - changelog/fixed
+    - title: Deprecated
+      labels:
+        - changelog/deprecated
+    - title: Removed
+      labels:
+        - changelog/removed
+    - title: Security
+      labels:
+        - changelog/security
+    - title: Dependencies
+      labels:
+        - changelog/dependencies