docs: allow publishing generated api cli docs

[mvidalgarcia]

Stems from #409 (review)

Current behavior

We have generate_cli_api.py script to generate the docs that go into https://docs.reana.io/reference/reana-client-cli-api/. ATM one has to manually copy the generated output to the corresponding file in docs.reana.io doing something like python scripts/generate_cli_api.py | pbcopy.

Desired behavior

Have the possibility to copy the autogenerated content to the docs.reana.io repo.

Solution

Add an option to copy the generated docs file automatically into docs.reana.io/docs/reference/reana-client-cli-api/index.md. RWC is doing something similar for the openapi specs.
Evaluate if it's worth converting the script into a mini click cli tool.