Move GitLab for Slack-related model code to FOSS
What does this MR do and why?
This change is part of #355896 (closed) to move all GitLab for Slack app code to FOSS.
This MR focuses on moving model code related to the GitLab for Slack app.
A changelog entry, and any documentation changes, will be added in the final MR.
There should be no functional changes.
MR acceptance checklist
This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.
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I have evaluated the MR acceptance checklist for this MR.
Related to #355896 (closed)
Edited by Luke Duncalfe