feat!: Fix meta service domains schema structure

[lrstanley]

Fixes: #3248.

BREAKING CHANGE: APIMeta.Domains changed from map to struct.

This should at least be a tiny bit less prone to breaking, as it only accounts for existing schema with that API, and future additions should silently be ignored (unless GitHub breaks the contract, which they didn't really do in this scenario).

• closes MetaService.Get fails because the schema of the JSON in the API response is different from the expected in APIMeta.Domains type #3248

[gmlewis]

(No need to force-push PRs in this repo, @lrstanley - as we always squash and merge.)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.95%. Comparing base (2b8c7fa) to head (af7c7fc).
Report is 103 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3249      +/-   ##
==========================================
- Coverage   97.72%   92.95%   -4.78%     
==========================================
  Files         153      171      +18     
  Lines       13390    11646    -1744     
==========================================
- Hits        13085    10825    -2260     
- Misses        215      727     +512     
- Partials       90       94       +4     

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[gmlewis]

Thank you, @lrstanley !
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

[tomfeigin]

LGTM

[gmlewis]

Thank you, @tomfeigin !
Merging.