Add cpp-oatpp-server generator (alpha)

[Kraust]

Don't know what the process is here for dealing with old issues, but I messaged in slack a day ago about this, and knocked an MVP out in that time, so I felt like seeing if there was interest in upstreaming this.

Original PR #7903

I have myself marked as the maintainer. I could go either way here. I have intentions on adding more to this in the future (I'm doing this for work as a skunkworks project right now). I also have interest in adding the client when I end up running into a need for it.

I intentionally did not implement anything in https://oatpp.io/docs/modules/oatpp-swagger/, nor did I break out multi-part form data. I can do both if the need arises, but I needed to meet a very strict deadline for a customer and those weren't necessary right now.

I originally wrote this for 7.0.0 (as that's what I target internally), there were only a few minor changes to the class to make this work on main.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

@ravinikam (2017/07) @stkrwork (2017/07) @etherealjoy (2018/02) @MartinDelille (2018/03) @muttleyxd (2019/08) @aminya (2025/05)

[Kraust]

@wing328 thanks for the suggestions, and good catch on adding the workflow because oat++ doesn't package a .pc file and I had to make tweaks to the cmake to get it working on Windows.

[wing328]

👍

let's give it a try

thanks for contributing a new generator

[wing328]

fyi. merged #21569 as a follow up PR with minor improvements