Add new KDF method docs `find_best_quote`

[smk762]

ref: GLEECBTC/komodo-defi-framework#2545 (comment)

[dimxy]

There is also previous (draft) version of this RPC merged earlier in this PR GLEECBTC/komodo-defi-framework#2362.
I'd suggest to add notes in the docs for the RPCs form that PR ("find_best_quote", "get_quotes_for_tokens", "execute_routed_trade") that they are reserved for future use and subject to change.