Keep ProposalProcedures in sorted order by the priority

Issue #3692 was implemented in #3698 in such a way that governance action states need to be sorted every time we do ratification. This is suboptimal, since it would be much better to keep the order of proposals in sorted order in the ConwayGovState and insert new proposals according to their priority. This would reduce the overhead on the epoch boundary, which is the time when we should really be cautious about performance.

Original discussion was on the PR: https://github.com/input-output-hk/cardano-ledger/pull/3698#pullrequestreview-1609208395