Reorganize how stargate docs source is stored

[polandll]

Currently, the antora modules are: ROOT, concepts, developers-guide and quickstart.
I plan to reorganize to:
ROOT
concepts - move the material here into ROOT
quickstart
install - docker, vm for each variant: C* 3, C* 4, DSE 6.8
connect
manage - starctl
develop - api-doc, api-graphql, api-rest, api-grpc, api-cql + dev tools; need to consider SDKs/SDK links
migrate - not sure I need this one
plan - what resources do you need to use stargate?
secure - REST auth, JWT

[polandll]

This plan has modified a bit, to include two components, core and apis. This facilitates multi-repo docset builds for Stargate and other docsets. An additional repo, datastax/adoc-howto is also included, to give users information on AsciiDoc, if they wish to contribute to the docs.

Component: core
Modules: ROOT, concepts, manage, install, migrate, plan, quickstart, secure (need connect, not currently there)

Component: apis
Modules: develop

Playbooks: site-local-sg.yaml, site-local-sg+adoc.yaml (collapse into just one, always build Stargate docs with the AsciiDoc how-to guide.

To build locally: (1) ln -s antora-sg.yml antora.yml in both components of the stargate/docs repo. Do the same in the datastax/adoc-howto repo. Then run the playbook with the command npm run build:localsg in your local stargate/docs directory.

[polandll]

Yet another change. The two components have been renamed stargate-core and stargate-develop. The work is in branch test-multi-repos. I need to modify the GH actions that are used to build and deploy the docs before I can merge into main.