Support Antora documentation

[alandefreitas]

This commit adds support for libraries with Antora documentation. In this workflow, each library can be an Antora component in an Antora master project hosted in another repository (https://github.com/cppalliance/site-docs) which also includes extra components with the user guide, contributor guide, and a component about the review process. At a later step, the antora documentation is merged with the existing in-source documentation generated with other tools.

[alandefreitas]

Amended

[sdarwin]

@alandefreitas,

• https://github.com/CPPAlliance/site-docs.git capitalization -> cppalliance

• Add an entry in the table https://github.com/boostorg/release-tools/blob/develop/docker/README.md . -v3. With a comment: 2023-10, installs nodejs, npm for antora builds.

I pushed cppalliance/boost_superproject_build:20.04-v3 up to dockerhub.

The next step is submitting a PR to boostorg/boost.

Switch v2 -> v3 in the image tag in https://github.com/boostorg/boost/blob/develop/.circleci/config.yml . Will you send them that? "New image to support antora builds in releases"

This pull request in release-tools shouldn't be merged until boostorg/boost is using the new image, that way the required packages will be available (npm, node) and antora won't crash due to missing dependencies.

[alandefreitas]

https://github.com/CPPAlliance/site-docs.git capitalization -> cppalliance

Well remembered. Luckily, these links are case-insensitive but I'll fix that.

Switch v2 -> v3 in the image tag

OK. So we'll do boostorg/boost first. I'll also update site-docs to contain 0 libraries in the antora playbook and test the whole workflow once again. Then I'll open the PR in boostorg/boost. boostorg/boost also has that extra complexity of divergent branches.

[alandefreitas]

https://github.com/boostorg/boost/pull/815