Build antora docs (main branch)

[abelsromero]

• Moved docs to an Antora structure under '/docs'

  • Created antora.yaml
  • Added nav.adoc respecting current structure.
  • Created modules 'ROOT' and 'apendices'
  • Moved source files to respective modules
  • Updated section level (reduced in 1)
  • Created soft link to include content from project sources

• Cleaned README.adoc

  • Removed un-used attributes
  • Updated content

• Removed now unnecessary elements:

  • Gradle docs modules
  • 'push-documentation' GH Action

• Fixes:

  • Fixed invalid references (I am not upgrading all references from legacy to modern in this PR)
  • Several typos & formatting

:information_source: Outside of the PR I renamed development-v3.x branch to maintenance-3.x, to align with the documentation done prior to my changes.