Move messages to stand-alone repo

[mattwynne]

[aurelien-reeves]

https://github.com/cucumber/messages

[aurelien-reeves]

Todo list (for at least go, java, javascript, perl, php and ruby - dotnet is ignored for now, elixir may require additional work in parallel of #1952):

• Add tests as part of the CI
  • Merge the perl PR after review
• Add code generation as part of dev workflow (still relying on make, but only dedicated to code generation)
• Check as part of the CI that generated code in the repo is up-to-date with the schemas
• Clean-up the repo
  • Synchronize READMEs accross languages to avoid package managers without READMEs
  • Write some doc / contributing doc
• Add release workflows (Release workflows messages#27)
  • Do not forget post-release processes
    • among others: java (done with polyglot release)
    • among others: php (dependency updates should be done using renovate or dependabot)
• Release
• Migrate issues / PRs

Depending on the status of the elixir piece of work, do not forget to

• Remove protocol buffer from elixir
  • in test-elixir.yml (WIP in a PR)

[mattwynne]

@aurelien-reeves thanks for all your work on this! I've had a busy few weeks and am only just picking this up. I don't quite have enough context to help with the task about synchronizing the readmes - do you mean we could copy / paste a standard README file manually into each language sub-folder? Or did you mean something more fancy and automated?

I've made a start on the release workflows, but we will need help from Wannes, Ciaran and Erik to get the Elixir, PHP and Perl releases working I think.

[aurelien-reeves]

@mattwynne regarding the readmes, I had no idea in mind. I just wanted to avoid missing readmes with npm or such package managers. That could be done manually.

For the release workflows:

• we don't care the for Elixir one at the moment: the actual implementation is not maintained, outdated, and unused. The next one is still WIP
• I am pretty sure we already have some Perl release workflow somewhere
• For PHP, this is based on git tags, like go-lang. This is using a sub-repo at the moment