feat(gitlab): Add platformCommit support for GitLab

[gauravluckme]

Changes

This PR implements the platformCommit: 'enabled' option for the GitLab platform, allowing Renovate to create commits via the GitLab Commits API instead of using git push.

Context

Please select one of the following:

• This closes an existing Issue, Closes: Add platformCommit support for GitLab #44225
• This doesn't close an Issue, but I accept the risk that this PR may be closed if maintainers disagree with its opening or implementation

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• Yes — substantive assistance (AI-generated non‑trivial portions of code, tests, or documentation).
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Documentation (please check one with an [x])

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The public repository:

[RahulGautamSingh]

you are not syncing git state after the platform commit has taken place. please, check the github flow and implement the same for gitlab