fix: return all json schema validation errors and expose Ajv types

[kimpers]

Description

By default Ajv only returns the first validation error, this fixes so that all errors are returned, and exposes the entire Ajv package under AJV to provide access to types etc.

Testing instructions

Types of changes

Checklist:

• Prefix PR title with [WIP] if necessary.
• Add tests to cover changes as needed.
• Update documentation as needed.
• Add new entries to the relevant CHANGELOG.jsons.

[xianny]

Suggestion: let's also delete all the relayer_api_*.json schemas. We never updated them for V4 and now they are broken, I think it's a sign that they should live in 0x-api repo.

resolved 👍