Epic: Account rekeying

[tac0turtle]

Summary

Account rekeying was proposed in adr-034.

Todo List:

• Implement account rekeying
• Adjust ADR (as needed)
• Review once open against upstream

[ValarDragon]

Really excited about this happening!!! Some of my thoughts on this since we first wrote the ADR are (And work I want to do with making hot keys sustainable):

We need to make account types able to define parsing logic for the change pubkey structs. e.g. I want to make an account type with multiple keys natively (Guardian keys, admin key, and a hot key). I should be able to use change pubkey to change just one of the keys. (Where my account type defined it)

I suspect this shouldn't be intense to do, we can probably just make change pubkey able to supply a set of (string, pubkey) pairs, and then every account type has parsing logic based on this.

[tac0turtle]

closing in favour of #14900