multi: support multiple RPC files

[guggero]

Updates the API docs with the following features:

• Make compatible with lnd and loop, generic enough to also easily include other projects in the future
• Include all *.proto files for gRPC
• Add service name in front of RPC, sort alphabetically
• Show both gRPC and REST on the same page
• Mention which protos are considered experimental and what that means
• Link to the proto files for easy access
• Mention commit the documentation was generated from
• Link to message type definition in protos
• List Enumerations (was a contributor PR that I included)
• Dockerize everything, removing the need to install a big list of tools/libraries just to generate the documentation

Also includes the commits of #8 and #10 because they seem to never have been looked at before.

[guggero]

I think this can be merged now? The official documentation is now generated and uploaded from this script.

[Roasbeef]

LGTM 🌭

One small thing to correct w.r.t how we sync the loop docs, will push a commit to fix that after this is merged.

[Roasbeef]

🤩