docs(mr): add synopsis and examples to mr commands

Description

Resolves the mr family findings from the style guide audit in #8263 (closed).

• Adds a Synopsis to the mr parent command.
• Adds Examples to mr approvers, mr todo, and mr view.
• Adds a Synopsis note to mr create explaining that the --recover flag is experimental and not ready for production use.

Each Synopsis is additive and does not repeat the Short description.

Commands updated:

• mr
• mr approvers
• mr todo
• mr view
• mr create

Content follows the documentation style guide and the GitLab CLI (glab) documentation style guide.

Related issues and merge requests

• docs: Fix CLI documentation inconsistencies ide... (#8263 - closed)

Documentation

If this MR adds or updates CLI command documentation, follow the conventions in the GitLab CLI (glab) documentation style guide, run make gen-docs, and commit the updated files in docs/source/.