Inconsistent build strategies across CI workflows

[Devansh-567]

• asciidoc-build.yml uses native asciidoctor install via install-asciidoctor-linux.sh
• any-branch-uploads.yml uses a Docker image p4lang/p4-spec-asciidoc:latest
• This means two different environments are building the same specs, potential for inconsistent output
• Propose unifying around one approach (Docker is the better pick, portable, reproducible)

[jafingerhut]

How is the Docker environment created that runs asciidoctor? Is that one generated in yet another script in a p4lang repository, or is it a Docker image created by other organizations that we use?

[Devansh-567]

The Docker image p4lang/p4-spec-asciidoc:latest used in any-branch-uploads.yml does not appear to have a publicly visible source, it returns 404 on Docker Hub and there is no corresponding repository in the p4lang GitHub org. This makes it difficult to audit what environment is actually being used to build the specs.
This further supports unifying around the native install approach used in asciidoc-build.yml instead, which uses install-asciidoctor-linux.sh and is fully transparent and version-controlled within this repository. That way the build environment is completely auditable and consistent across both workflows.

[jafingerhut]

I have no objections to using a Github action that executes install-asciidoctor-linux.sh as a setup step. It is the same set of install steps we recommend that individuals use if they want to run Asciidoctor to test building the spec locally on their own systems.