Commit modal: condense commit confirmation alert

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Context

In !206943 (comment 2807517380), the success confirmation that appears after the user edits a file and commits changes was condensed.

My only concern would be the loss of the Create merge request button in the new success banner. This gives users a clear path forward, and encourages the usage of merge requests for good development hygiene / encouraging more usage of the tools in GitLab's ecosystem.

Before	After

Design recommendation

Update the text in the banner, and add the Create merge request button if the user did not create a merge request:

User did create a merge request	User did NOT create a merge request
You successfully committed and pushed your changes to branch-name-here [copy button].	You successfully committed and pushed your changes to branch-name-here [copy button]. Create merge request