Pass documentation sources based on client capabilities instead of custom initialization option

[jakebailey]

Currently, we accept in our initialization options the markup kind to use for all calls. LSP has its own options given in the client capabilities for this, which we should use instead.

https://github.com/Microsoft/python-language-server/blob/037d2485f5b5de16eee87e7adff2e1efbca0b859/src/LanguageServer/Impl/Implementation/Server.cs#L127-L136

Each of those sources can be given their own documentation source.