Fix: mr description edited tooltip locale

What does this MR do and why?

Right now the Merge Request description section is not been implemented by Vue, and the code for the edited text was quite old for more than 6 years, this MR is meant to align the edited text section with other issuable edited text section.

/cc @prajnamas @qk44077907 @orozot

Fix: mr description edited tooltip locale

• Replace hardcoded texts with translations.
• Replace the variable object to a explicit name merge_request.

Changelog: fixed

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

• Pre-request: Change preferred language to any language other than English.

1. Go to any Merge request
2. Try to modify the description
3. Save the changes
4. Observe

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.