Implement JSON-RPC API namespace separation in documentation

[bomanaps]

This closes #655, am yet to remove the initial JSON-RPC

[lightclient]

Can we auto generate these? Would rather not need to manually add new methods into the sidebar each time. Also the direct links to the method doesn't work for me, seems to be missing a /docs prefix.

[zcstarr]

Actually missed this amongst things in PRs, as we're looking at the refactoring of docs , this is a nice feature to be able to drill down methods by some logical grouping. I think the way forward for this would be to add tags for all the methods, and we can add a open-rpc linter rule for that I think (' something like at least 1 tag required').

with an new rule to the new linter, so people writing specs must include a tag with the method. That would allow for the categorization to be a part of the spec, and the we can present that in the view layer or not, however view layers would like to consume it. I think it would just be a consumption signal and something devs can grep for or even code against to filter, and would be more resilient than naming convention, especially if it bridges multiple concerns.

https://spec.open-rpc.org/#tag-object
We'd probably want to make a tags.yml and then reference those tags in the relevant methods. it'd make the docs really consistent .

An example tag here:

[fjl]

I think this is now resolved with merging #725