feat(gitlab): add branch status check attemps

[philippe-granet]

Changes

• Add branch status check attemps before trying to add status check
• Allow overriding the branch status check attempts via experimental env RENOVATE_X_GITLAB_BRANCH_STATUS_CHECK_ATTEMPS.

Context

• GitLab external job "renovate/stability-days" treated as passing status check even when tests fail #27111
• feat(platform/gitlab): Allow custom delay for pipeline status via experimental variable #23239
• GitLab: Two pipelines per MR #5743

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository