feat(plugins): add `roadrunner-plugins` repository

[rustatian]

Reason for This PR

• Maintain all RR plugins in a separate repository.

Description of Changes

• Introduce roadrunner-plugins repository.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.] [Reviewer TODO: Verify that these criteria are met. Request changes if not]

• [x] All commits in this PR are signed (git commit -s).
• [x] The reason for this PR is clearly provided (issue no. or explanation).
• [x] The description of changes is clear and encompassing.
• [x] Any required documentation changes (code and docs) are included in this PR.
• [x] Any user-facing changes are mentioned in CHANGELOG.md.
• [x] All added/changed functionality is tested.

[codecov[bot]]

Codecov Report

Merging #99 (03f795e) into master (715d3bd) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #99   +/-   ##
=======================================
  Coverage   43.18%   43.18%           
=======================================
  Files          12       12           
  Lines         558      558           
=======================================
  Hits          241      241           
  Misses        306      306           
  Partials       11       11           

Impacted Files	Coverage Δ
internal/cli/reset/command.go	5.88% <ø> (ø)
internal/cli/root.go	69.84% <ø> (ø)
internal/cli/serve/command.go	6.25% <ø> (ø)
internal/cli/workers/command.go	19.14% <ø> (ø)
internal/cli/workers/render.go	0.00% <ø> (ø)
internal/container/config.go	89.09% <ø> (ø)
internal/container/plugins.go	100.00% <ø> (ø)
internal/rpc/client.go	100.00% <ø> (ø)

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