Allow searching issues for strings containing colons

What does this MR do?

Allow searching for strings with colons - only tokenize keys in FilteredSearchTokenKeys.tokenKeys

Are there points in the code the reviewer needs to double check?

• Are there other filter values allowed that aren't handled in frontend?

Why was this MR needed?

Searching double colon can be common for code snippets

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #28357 (closed)