[docs/rpc] rpc method examples curl to localhost not a public endpoint

[Nick Frostbutter]

Problem

The rpc docs give examples of how to use each method using a CURL request to a localhost endpoint, which assumes a user is already running a local test validator. Which the grand majority will not.

Proposed Solution

Update all the rpc CURL examples to use the public devnet endpoint instead of localhost. This will allow anyone to run the command right away and get a real response. This might involve updating some of the request params to use accounts and data that is live on devnet