Audit key management + key rotation logic and testing

[alecps]

• [x] Consider moving requestHasValidKeyVersion, getRequestKeyVersion, getResponseKeyVersion, etc. into common pkg
• [x] Generate new domains polynomials if necessary
• [x] Add new error for unsupported key versions and make sure it's being used
• [x] Audit key rotation logic and add any necessary tests

Output:

• Unit tests that check this part of the protocol

[arthurgousset]

Sprint planning:

• signers have different versions of keys in key store
• Combiner deals with key versions it accepts
• Tricky because this was it's own PR and sort of warrants its own review (was a while back) to see if it still makes sense.
• Could potentially ask Victor to help, but Alec wrote most of it
• It's difficult to test key rotation logic, thinking about the methodology is the biggest effort here

Poker:

• Izzy - Reading code you wrote a while back can be tricky
• Alec - "Generate new domains polynomials if necessary" is a bit confusing (might need some help from victor)
• Eela - could we do this after merging to master, can we do this later
• Alec - We'll want an E2E in staging
• Alec - This might become a major re-write of mock key store

[arthurgousset]

Sprint planning:

• Alec - probably knocked off 1 dev day here. Still work outstanding on mock keystore. Happy with current estimat

[arthurgousset]

Sprint check-in:

• Alec started working on this (good sense of work)

[arthurgousset]

Sprint planning:

• Alec working on this atm

[alecps]

https://github.com/celo-org/celo-monorepo/pull/9958