WIP - Working on remote-settings client compatibility

[alexcottner]

Work In Progress

Ignore this for now...

To-Do

• Remove old remote-settings client, which uses endpoints and logic that are not supported
• Rename objects/structs to avoid old vs new naming
• Update any app-services components that were using the legacy client
• Add any missing functionality to new remote-settings client
• Update implementations in consumer applications

Follow-ups

• Increase poll frequency of new remote-settings client
• Add v2 service support
• Add signature agility
• Add glean telemetry

Pull Request checklist

• Breaking changes: This PR follows our breaking change policy
  • This PR follows the breaking change policy:
    • There are corresponding PRs for our consumer applications that resolve the breaking changes and have been approved
    • TODO: create and list those here...
• 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.