Feature request: Add p2pool ``--rpc-login USER:[PASS]`` argument
## OS & Version:
Windows 11, Gupax v1.3.10

I personally host my monero node on another machine so that I don't have to worry about storing the huge monero ledger on my main computer. It's also nice to use it to sync my phone wallet to a node I trust.

I set a simple RPC logon password on it so that I can ensure I would be the only one with access to it. Although it appears, Gypax does not natively support this and requires passing it in via the "Command Arguments" options. Which appears to make p2pool never go green and makes it so that its info is not nicely shown on the ``status`` page (or this is a side effect of #120)

This arg is simple, required username with optional password.