feat(wallet-service): added read-only authorizer and api

[andreabadesso]

Implements https://github.com/HathorNetwork/internal-rfcs/pull/39

Acceptance Criteria

• We must be able to generate JWTs for read-only wallets (using xpubkeys)
• Wallets must be in the READY state in order to authenticate, we must error otherwise.
• APIs that mutate database state must be marked as write and we should reject requests made using a read-only JWT.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged
• Make sure either the unit tests and/or the QA tests are capable of testing the new features
• Make sure you do not include new dependencies in the project unless strictly necessary and do not include dev-dependencies as production ones. More dependencies increase the possibility of one of them being hijacked and affecting us.