[Thunderstore] Add Thunderstore Badges (#9782)

* add base for thunderstore services

* badge service and corresponding tester for thunderstore download count

* badge service and corresponding tester for thunderstore latest package version

* fix HTML

* use stable package-metrics endpoint

* remove erroneous statement from docs

* remove `namedLogo` from default badge data on both services

* follow route naming conventions

* use `[x].json` for test assertions

* use existing version pattern

* document service `handle` return-type more narrowly

* use consistent test formatting

* add base for thunderstore services

* badge service and corresponding tester for thunderstore download count

* badge service and corresponding tester for thunderstore latest package version

* fix HTML

* use stable package-metrics endpoint

* remove erroneous statement from docs

* remove `namedLogo` from default badge data on both services

* follow route naming conventions

* use `[x].json` for test assertions

* use existing version pattern

* document service `handle` return-type more narrowly

* use consistent test formatting

* plural-ise base thunderstore docs

* don't require unused attributes

* declare BaseThunderstoreService abstract, add docstring

* add thunderstoreGreen static variable

* add thunderstore likes service

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Co-authored-by: chris48s <chris48s@users.noreply.github.com>