chore: renovate upgrade per component

Separate renovate upgrade per component, for api/*, front/*, and docs/* packages files.

.gitlab/renovate.json

@@ -14,6 +14,10 @@
   "rangeStrategy": "pin",
   "ignoreDeps": ["$CI_REGISTRY/funkwhale/backend-test-docker"],
   "packageRules": [
+    {
+      "matchPaths": ["api/*", "front/*", "docs/*"],
+      "additionalBranchPrefix": "{{parentDir}}-"
+    },
     {
       "matchUpdateTypes": ["major", "minor"],
       "matchBaseBranches": ["stable"],