Prepare repository for next .github release and SBT build improvements

[alejandrohdezma]

What has been done in this PR?

Prepare project for next .github release

• Add ci-publish command alias that will be used instead of ci-release for publishing artifacts.
• Move docs templates to docs folder (as mdoc is expected).
• Move microsite files to microsite folder.
• Run github before ci-docs & ci-publish.
• Remove ci-microsite (it gets inline in ci-docs).
• Add actions.yml file that will be used by next .github release workflows to read pre/post conditions to run before/after ci-* commands.

Simplify SBT build

• Re-order settings.
• Remove unneeded settings.
• Remove old sbt-org-policies markers.
• Add sbt-remove-test-from-pom to avoid publishing test dependencies to POM.
• Add sbt-codecov to run tests with coverage and auto-upload to Codecov.

Update versions

• Update plugins to latest versions
• Update Scala versions to 2.13.2/2.12.11

[codecov]

Codecov Report

Merging #501 into master will increase coverage by 11.17%.
The diff coverage is 81.25%.

@@             Coverage Diff             @@
##           master     #501       +/-   ##
===========================================
+ Coverage   79.19%   90.37%   +11.17%     
===========================================
  Files          23       24        +1     
  Lines         548      613       +65     
  Branches        2        3        +1     
===========================================
+ Hits          434      554      +120     
+ Misses        114       59       -55     

Impacted Files	Coverage Δ
github4s/src/main/scala/github4s/Github.scala	100.00% <ø> (+100.00%)	⬆️
...hub4s/src/main/scala/github4s/GithubIOSyntax.scala	0.00% <ø> (ø)
...s/src/main/scala/github4s/domain/PullRequest.scala	100.00% <ø> (+100.00%)	⬆️
...4s/src/main/scala/github4s/domain/Repository.scala	100.00% <ø> (ø)
...s/src/main/scala/github4s/domain/SearchParam.scala	16.66% <ø> (ø)
.../src/main/scala/github4s/http/RequestBuilder.scala	100.00% <ø> (+100.00%)	⬆️
.../github4s/interpreters/ActivitiesInterpreter.scala	100.00% <ø> (ø)
...scala/github4s/interpreters/GistsInterpreter.scala	100.00% <ø> (ø)
...thub4s/interpreters/OrganizationsInterpreter.scala	100.00% <ø> (ø)
...ithub4s/interpreters/PullRequestsInterpreter.scala	100.00% <ø> (ø)
... and 26 more

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[BenFradet]

LGTM 👍