Handle declined event for bitbucket server importer

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What does this MR do and why?

Handle declined event for bitbucket server importer. As discussed in this thread:

• Add "Closed by" actor
• Add the note

Changelog: added

Notes

• We need to manually use MergeRequest::Metrics.find_or_initialize_by (similar with BitbucketServerImport::Importers::PullRequestNotes::ApprovedEvent), because:
  • The metric does not exist yet because callback in MergeRequest model is disabled for import
• Changes are only made on the new code path. The old one BitbucketServerImport::Importers::PullRequestNotesImporter is not adjusted. See:
  • #451129 (comment 1904398430)
  • #456262

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Before	After

How to set up and validate locally

1. Initial environment setup can follow this
2. Prepare some data in Bitbucket Server (create a DECLINED MR)
3. Patch the code to allow localhost connection to Bitbucket Server local:

diff --git a/gems/gitlab-http/lib/gitlab/http_v2/url_blocker.rb b/gems/gitlab-http/lib/gitlab/http_v2/url_blocker.rb
index 99876c779539..06bd0c6b92cd 100644
--- a/gems/gitlab-http/lib/gitlab/http_v2/url_blocker.rb
+++ b/gems/gitlab-http/lib/gitlab/http_v2/url_blocker.rb
@@ -64,6 +64,9 @@ def validate_url_with_proxy!(
         )
           # rubocop:enable Metrics/ParameterLists
 
+          allow_localhost = true
+          allow_local_network = true
+
           return Result.new(nil, nil, true) if url.nil?
 
           raise ArgumentError, 'The schemes is a required argument' if schemes.blank?

4. Tail the log file: tail -f log/importer.log
5. Go to http://127.0.0.1:3000/import/bitbucket_server/status
6. Click Import
7. Check the DECLINED MR, should have an author (if the author exist in GitLab)