Add metadata_delete_search_terms method to delete search terms in history metadata

[cyndichin]

Pull Request checklist

This patch adds a new method metadata_delete_search_terms that deletes the entries in the moz_places_metadata_search_queries table. This is to support a new feature in which we want to delete the search terms stored instead of deleting the entire history metadata.

• Breaking changes: This PR follows our breaking change policy
  • This PR follows the breaking change policy:
    • This PR has no breaking API changes, or
    • There are corresponding PRs for our consumer applications that resolve the breaking changes and have been approved
• Quality: This PR builds and tests run cleanly
  • Note:
    • For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
    • If this pull request includes a breaking change, consider cutting a new release after merging.
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry in CHANGELOG.md or an explanation of why it does not need one
  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• Dependencies: This PR follows our dependency management guidelines
  • Any new dependencies are accompanied by a summary of the due diligence applied in selecting them.

[cyndichin]

@mhammond This is my first Rust PR, so let me know if there is anything that I missed! We want to add a new method to only delete search term entries and not all of the history metadata entries. This is because we want to allow users to clear / delete their recent search terms without needing to impact other entries.

thanks to @issammani for helping me along the way.

[mhammond]

This looks good, thanks!