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.
• Simplify modules by using the following features from SBT:
  • Auto-root project
  • project macro for setting project's name and baseDirectory (using the name of the lazy val)
  • Since we only have shared code in our cross-compiled modules use CrossType.Pure instead.
• 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 docs

• Add a table of contents to README.md

Update versions

• Update plugins to latest versions
• Update Scala version to 2.13.2

[codecov]

Codecov Report

Merging #335 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #335   +/-   ##
=======================================
  Coverage   68.56%   68.56%           
=======================================
  Files           8        8           
  Lines         299      299           
  Branches        3        4    +1     
=======================================
  Hits          205      205           
  Misses         94       94           

Impacted Files	Coverage Δ
fetch-debug/src/main/scala/debug.scala	0.00% <ø> (ø)
fetch-debug/src/main/scala/document.scala	0.00% <ø> (ø)
fetch/src/main/scala/cache.scala	100.00% <ø> (ø)
fetch/src/main/scala/datasource.scala	100.00% <ø> (ø)
fetch/src/main/scala/execution.scala	100.00% <ø> (ø)
fetch/src/main/scala/fetch.scala	91.04% <ø> (ø)
fetch/src/main/scala/log.scala	66.66% <ø> (ø)
fetch/src/main/scala/syntax.scala	100.00% <ø> (ø)

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[juanpedromoreno]

Thanks @alejandrohdezma !