feat/catalog-backend-module-gitlab: create url location only if file exists (fixes #3)

Signed-off-by: Ruslan.Nasyrov <goququ@ya.ru>

docs/integrations/gitlab/discovery.md

@@ -49,7 +49,7 @@ of your backend.
 +  builder.addProcessor(
 +    GitLabDiscoveryProcessor.fromConfig(env.config, {
 +       logger: env.logger,
-+       skipReposWithoutExactFileMatch: true,
++       skipReposWithoutExactFileMatch: false,
 +    })
 +  );
 ```

plugins/catalog-backend-module-gitlab/src/lib/client.ts

@@ -80,6 +80,13 @@ export class GitLabClient {
     });
 
     if (!response.ok) {
+      if (response.status >= 500) {
+        this.logger.debug(
+          `Unexpected response when fetching ${request.toString()}. Expected 200 but got ${
+            response.status
+          } - ${response.statusText}`,
+        );
+      }
       return false;
     }