New plugin: "plugin-catalog-backend-module-gerrit"

The "plugin-catalog-backend-module-gerrit" exports an entity
provider for discovering catalog entities from Gerrit
repositories. The provider uses the "List Projects" API in Gerrit
to get a list of repositories and will automatically ingest all
"catalog-info.yaml" files stored in the root of the matching
projects.

Also added the "getGerritProjectsApiUrl" function to the Gerrit
integration. This returns the url to the "List Projects" API for
a given integration.

Signed-off-by: Niklas Aronsson <niklasar@axis.com>

microsite/sidebars.json

@@ -156,7 +156,10 @@
       {
         "type": "subcategory",
         "label": "Gerrit",
-        "ids": ["integrations/gerrit/locations"]
+        "ids": [
+          "integrations/gerrit/locations",
+          "integrations/gerrit/discovery"
+        ]
       },
       {
         "type": "subcategory",