feat!: identity public key purpose and security levels

[antouhou]

Issue being fixed or feature implemented

Identity multikeys as per DIP-11: https://github.com/dashpay/dips/blob/master/dip-0011.md#keys

What was done?

• Add purpose and securityLevel fields to public keys
• Change identity facade to accept raw public key objects instead of public key data
• Add three enums with purposes, security levels and allowed combinations of them
• Changed public key validation function to check that the security level is in the allowed range for a specific key purpose
• Updated fixtures to include all the changes

How Has This Been Tested?

Run the tests, add some new tests

Breaking Changes

dpp.identity.create now accepts a raw public key object instead of just public key data blob

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[shumkov]

LGTM! 👍