Rename search_scope to search_level

What does this MR do and why?

Related to #479404 (closed)

The what: This MR changes all instances of the option key named search_scope in the backend code that references values of global, group, and project to the name search_level.

It unfortunately required a lot of spec updates so that's why the MR is so big.

While working on this I found a bug with the by_archived search filter where the project level searches were not working correctly and fixed/updated the spec

The why: I'd rather do this now than later where the update will be too hard. It will help other developers adding things to Advanced search to have a consistent meaning for what search_level and search_scope mean.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

N/A - backend changes only

How to set up and validate locally

This touches too many search scopes to provide detailed testing instructions.

What you could do is perform global, group, and project search for every search scope and validate that it works.

note: gdk must be enabled for elasticsearch and fully indexed