fix(collections): implement ListCollections, which returned 501

api/openapiv2/restcol.swagger.json

@@ -807,7 +807,17 @@
       "description": "Message that represents an arbitrary HTTP body. It should only be used for\npayload formats that can't be represented as JSON, such as raw binary or\nan HTML page.\n\n\nThis message can be used both in streaming and non-streaming API methods in\nthe request as well as the response.\n\nIt can be used as a top-level request field, which is convenient if one\nwants to extract parameters from either the URL or HTTP template into the\nrequest fields and also want access to the raw HTTP body.\n\nExample:\n\n    message GetResourceRequest {\n      // A unique request id.\n      string request_id = 1;\n\n      // The raw HTTP body is bound to this field.\n      google.api.HttpBody http_body = 2;\n\n    }\n\n    service ResourceService {\n      rpc GetResource(GetResourceRequest)\n        returns (google.api.HttpBody);\n      rpc UpdateResource(google.api.HttpBody)\n        returns (google.protobuf.Empty);\n\n    }\n\nExample with streaming methods:\n\n    service CaldavService {\n      rpc GetCalendar(stream google.api.HttpBody)\n        returns (stream google.api.HttpBody);\n      rpc UpdateCalendar(stream google.api.HttpBody)\n        returns (stream google.api.HttpBody);\n\n    }\n\nUse of this type only changes how the request and response bodies are\nhandled, all other features will continue to work unchanged."
     },
     "apiListCollectionsResponse": {
-      "type": "object"
+      "type": "object",
+      "properties": {
+        "collections": {
+          "type": "array",
+          "items": {
+            "type": "object",
+            "$ref": "#/definitions/apiGetCollectionResponse"
+          },
+          "description": "The project's collections, newest first.\n\nDeliberately the SAME message the single-collection GET returns, rather\nthan a slimmer summary type. ListByProjectID already preloads each\ncollection's latest schema and its fields - a summary type would throw\naway data that has already been read, and would give a client two shapes\nto parse for one resource, which is how the two drift.\n\n\"Latest schema\" is also what makes this a list of COLLECTIONS and not of\ncollection-versions: the storage query limits the preload to one schema\nper collection.\n\nNo pagination fields yet. Adding them later is backwards-compatible in\nproto3; shipping page_size and page_token that nothing honours is not -\nit tells a client the endpoint is paginated when it is not."
+        }
+      }
     },
     "apiQueryDocumentResponse": {
       "type": "object",