Add Socks v5 support to daemon and wallet

[vtnerd]

Socks v5 adds IPv6 support and basic username/password authentication. The user/pass authentication is a cheap way to prevent rogue applications from requesting proxied connections. Tor and SSH do not support authentication but I2P, Nym, and Dante do.

When I started this implementation, I didn't know Nym added Socks v4 support. This makes the patch somewhat less useful, as the original #8562 Socks v5 request was for Nym support. This patch might want to be rejected on that reason alone - the only useful features are user/pass and IPv6.

This includes a fairly extensive explanation of proxies in the daemon and cli wallets, so that might be useful for keeping regardless.

[vtnerd]

Crap, looks like older versions of boost don't have some ASIO functionality I used. Crap, will have to update.

[tobtoht]

What would be the minimum Boost version for this PR?

Is it time to undust #9162 and bump the minimum Boost requirement?

[vtnerd]

The minimum version for this feature would be 1.67. In this case, its not really critical, I should be able to work-around it.

[iamamyth]

After many years, IPv6 has started to see substantial, and increasing, adoption, so I think this would be a reasonable addition. However, it's not urgent, and, based on the comments in #9162, I think you could safely assume Boost 1.67 (Ubuntu 18.04 continues to wither) and roll out this feature after a boost version upgrade to 1.67. Of course, you can do the extra work to support the current Boost version, but you may very well have better uses for your time.

[vtnerd]

I just pushed a change to fix the Boost issues. Everything looks good for that.

The functional tests failed, but it looks spurious right now. Testing locally to confirm, and may just push a dummy update to re-run the tests.

[vtnerd]

Good for review!

[sneurlax]

Adds SOCKSv5 support with tests and documentation included. Tested working. The code looks relatively minimal such that I don't see anything to remove, really. I don't see any potential privacy or security concerns, LGTM

[sneurlax]

Closes #9443