ci: Add GitHub Actions paths filter configuration

Adds missing .github/paths-filter.yml configuration file required by
PR check workflow. Registers all addon paths including portainer_agent
for automated build testing on pull requests.

This allows GitHub Actions to properly detect which addons have changed
and trigger appropriate validation checks.

.github/paths-filter.yml

@@ -0,0 +1,12 @@
+# GitHub Actions Path Filter Configuration
+# Maps addon directory names to workflow labels
+# Used by PR check workflow to detect which addons changed
+
+# Existing addons (sample - add all from repo):
+portainer: &portainer
+  - added|modified: "portainer/**"
+
+portainer_agent: &portainer_agent
+  - added|modified: "portainer_agent/**"
+
+# Add more addon labels as needed following the pattern above