Allow creating deploy keys with an expiry date

What does this MR do and why?

This MR creates an "Expires At" control for Deploy Keys, allowing users to specify an expiry date in the same way they do for personal SSH keys.

Screenshots or screen recordings

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Current outstanding work

• Add the expiration picker to the form
• Have initial tests pass
• Have the deploy keys expiration date picker use the correct theme.
• Add additional tests to prove the expiration or lack thereof is correctly applied
• validate current UI choices match GitLab standards
• Check text and translation
• Email Project Owners when a key is about to expire (same as for Deploy Tokens)
• Update any documentation

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.

Related to #378367 (closed)