feat: enums and arrays on new ctype metaschema

[rflechtner]

fixes KILTProtocol/ticket#2456

Amends the new CType metaschema with new features:

• Allowable values for properties of string, number & integer types can be restricted with an enum validator.
• Arrays are allowed, with all items validating against a schema normally used to validate simple properties (i.e., boolean, string, or number, schema, or a CType reference).
• Length assertions are allowed for arrays and strings.
• Maximum and minimum value assertions are allowed for numbers and integers.

How to test:

It's easiest to play with the metaschema (which you can also download from https://gateway.pinata.cloud/ipfs/bafybeiah66wbkhqbqn7idkostj2iqyan2tstc4tpqt65udlhimd7hcxjyq) by validating your desired CTypes against it on https://www.jsonschemavalidator.net.

Checklist:

• I have verified that the code works
• I have verified that the code is easy to understand
  • If not, I have left a well-balanced amount of inline comments
• I have left the code in a better state
• I have documented the changes (where applicable)

[ntn-x2]

Looks good to me! Just a question: I guess this definition does not allow for nested object definitions, right?