docs(all): integrated documentation using canonical MkDocs template

[VRamakrishna]

• Moved old docs folder containing source files for legacy Cactus documentation to docs-cactus.
• Created new docs folder using the MkDocs template specified in https://github.com/tkuhrt/documentation-template as the base.
  • Created overview files with useful links, diagrams, and references, for new and existing users
  • Migrated older Cactus and Weaver documentation for getting hands-on with code and samples to the new website, available through separate tabs
  • Fixed formatting, image references and other URLs, and organization
  • Created several stub files with temporary links, to be filled and expanded upon in due course, drawing on content already present in the above legacy documents
• Added a GitHub action to automatically push the documentation build (generated using mkdocs) to the gh-pages branch, and then publish those the hyperledger organization's GitHub page for Cacti.
  • To get an idea of how this looks and feels, see https://vramakrishna.github.io/cacti/, where these docs are currently being served from.
• Updated Discord handles for maintainers in the MAINTAINERS.md file.
• Fixed formatting typos in old doc files.

[VRamakrishna]

Please comment here if you would like to add or remove pages from the current website (sample: https://vramakrishna.github.io/cacti/).

There's a lot more we need to do to enhance this website, including filling in content wherever needed, removing redundant content, reorganizing the Cactus and Weaver pages into a common set of pages where we show how the different Cacti packages and transaction pipelines can be instantiated and tested, and providing more detailed info on releases and roadmap.

For these, I think we can open issues and divide tasks among ourselves. For now, let us publish the documentation, just making sure there is no incorrect or misleading info there.

[petermetz]

@VRamakrishna LGTM, thank you very much for working on the merged documentation!

[izuru0]

LGTM!