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) & 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.
• Add sbt-remove-test-from-pom to avoid publishing test dependencies to POM.
• Add sbt-modules to simplify build.
  • Move all "modules" inside modules directory
• Add sbt-codecov to run tests with coverage and auto-upload to Codecov.

Improve documentation

• Add README template
• Remove old sbt-org-policies markers.

Update versions

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

[codecov]

Codecov Report

Merging #148 into master will decrease coverage by 1.91%.
The diff coverage is 80.95%.

@@            Coverage Diff             @@
##           master     #148      +/-   ##
==========================================
- Coverage   97.60%   95.68%   -1.92%     
==========================================
  Files          10       10              
  Lines         125      139      +14     
  Branches        4        2       -2     
==========================================
+ Hits          122      133      +11     
- Misses          3        6       +3     

Impacted Files	Coverage Δ
...ysevendeg/scalacheck/combinators/Combinators.scala	100.00% <ø> (ø)
...ortysevendeg/scalacheck/datetime/GenDateTime.scala	80.00% <ø> (ø)
...ysevendeg/scalacheck/datetime/instances/joda.scala	100.00% <ø> (ø)
...scalacheck/datetime/jdk8/granularity/package.scala	100.00% <ø> (ø)
...scalacheck/datetime/joda/granularity/package.scala	100.00% <ø> (ø)
...ala/com/fortysevendeg/scalacheck/magic/Magic.scala	100.00% <ø> (ø)
...ysevendeg/scalacheck/datetime/instances/jdk8.scala	70.00% <50.00%> (ø)
...rtysevendeg/scalacheck/datetime/joda/GenJoda.scala	94.44% <50.00%> (ø)
...ortysevendeg/scalacheck/datetime/Granularity.scala	100.00% <100.00%> (ø)
...rtysevendeg/scalacheck/datetime/jdk8/GenJdk8.scala	100.00% <100.00%> (ø)
... and 1 more

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[juanpedromoreno]

Great cleanup! Thanks @alejandrohdezma !