feat: add self trade tx type, volume & limits checks

[vindard]

Description

This PR is to separate self-trade transaction types from other intraledger transactions. The goal here is to have separate limits for self-trades vs. other intraledger transfers.

It also separates out a new "send-lightning-limits" test file and adds a comprehensive set of tests around limits (now possible because of #1518).

I also did some cleanup and added new methods to our integrations tests to generate wallets/accounts on the fly to make each limits test a bit more self-contained. Before now, we would use wallets that were previously instantiated and used in other tests which created dependencies across different testing functions.