Add committee change events

[ixje]

#2754 added events for candidate registration and voting. In the discussion there @roman-khimov suggested (https://github.com/neo-project/neo/pull/2754#issuecomment-1136329619) adding events for committee changes. So far I didn't see an issue for it so here's one to make sure it's not forgotten.

Neo Version

• Neo 3

Where in the software does this update applies to?

• Ledger