Truncate long MR description

Closing as something we won't do because truncation of the merge request description would negatively impact the outcome of minimizing the time it takes a reviewer to understand the context of a merge request. Full explanation in this comment #430730 (comment 1969821421).

Even the original issue description mentions that this is only an interim step to a larger reorg of info and widgets on the page. These are the issues/epics to follow on how we are looking to solve this:

• Merge request overview tab improvements to conv... (&13632)
• Consolidate merge request main actions in one p... (&6553).

Original description

Problem to Solve

Long MR descriptions make it harder to find common actions on the page since there isn't a fixed location for items. In particular this obscures the common merge widgets which provide valuable information to the status of an MR and how to move it forward.

Proposal

Following the pattern of !144819 (merged), we should truncate the description of merge requests. This would provide UX alignment across items as well as make it easier to find things.

This could be an interim step to a larger reorganization of information and the widgets on the page.

We should feature-flag it.