Starting new Remote Settings API

[bendk]

Implemented client functionality and started the general structure for the types. The big item left todo is storage.

Added a CLI to test it, you can run it using cargo rs.

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  • This PR follows the breaking change policy:
    • This PR has no breaking API changes, or
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Branch builds: add [firefox-android: branch-name] to the PR title.

[bendk]

This new API is still a WIP, but I think we still could merge this since no consumers are using it yet. I tested it with the cargo rs CLI and it seemed to work.

@leplatrem I added you as a reviewer mostly to make sure that the client code is hitting the right endpoints and following the client specs correctly.

[bendk]

I believe that Storage will want to use &mut in a lot of its methods, since that's what rusqlite::Connection::transaction() uses and in general we want exclusive access to the connection. But I'm not totally sure this is right and maybe we should move it outside the mutex.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 214 lines in your changes missing coverage. Please review.

Project coverage is 21.83%. Comparing base (eb1f268) to head (78ba5d2).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
components/remote_settings/src/client.rs	0.00%	104 Missing ⚠️
components/remote_settings/src/service.rs	0.00%	54 Missing ⚠️
components/remote_settings/src/lib.rs	0.00%	32 Missing ⚠️
components/remote_settings/src/storage.rs	0.00%	24 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6417      +/-   ##
==========================================
- Coverage   21.99%   21.83%   -0.16%     
==========================================
  Files         342      344       +2     
  Lines       30729    30951     +222     
==========================================
  Hits         6759     6759              
- Misses      23970    24192     +222     

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