[Search] Add search approaches content, rename querying-for-search doc

[leemthompo]

Added new content to search-approaches.md

• 👁️PREVIEW

Updated page name/links:

• querying-for-search-searching-with-the-search-api.md was renamed to querying-for-search.md.
  • all links have been updated (this section needs to be fleshed out with subpages in subsequent PRs and references checked for relevance)
  • Also changed title from "Querying for search / searching with the search API" to "Query languages for search"

FYI

I tried using docs-builder mv to rename the querying-for-search file but I couldn't get it working and ran out of time, so just manually updated links

[florent-leborgne]

🚗