[Python][FastAPI] Added support for library mode

[AdityaMayukhSom]

This PR fixes #21079. This PR added one more config option isLibrary to FastAPI generator, which is defaulted to false to remain backwards compatible. In library mode, the docker and compose files are not generated and the security API functions use abstract base class to delegate security functionalities. On top of that, this PR also includes parent class ABC to all the base API classes in library mode to ensure all the implementing child classes must implement all the defined methods from the base class.

cc: @multani @fa0311 @krjakbrjak @tomplus @cbornet Can you please look into the PR and if everything is alright, merge this?

PR checklist

• Read the contribution guidelines.
• 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 Git BASH)
  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.
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[AdityaMayukhSom]

@wing328 Can you please review this PR?

[wing328]

thanks for the PR

we need another samples to test the option

please clone ./bin/configs/python-fastapi.yaml to test the option. add the new samples to this PR

and update the workflow .github/workflows/samples-python-server.yaml accordingly

[wing328]

closed via #21079 (comment)