[Feature] Mutator Hooks

[VisargD]

Gateway currently allow hooks of type guardrail. These hooks perform various checks and validations and then return a boolean verdict. But there are various use cases where the context of request needs to be transformed based on hook results. In order to achieve this, we will be introducing a new type of hook called mutator.

Mutator hooks will have the capability of transforming the request and response instead of just passing a verdict. These hooks can then be used for various use cases like PII redaction, PHI redaction, Regex based redaction, etc. And these hooks can also be further extended to implement custom logic like abstracting out the configs and provider configs.

For the first release, we will be implementing it for the redaction use case for existing plugins like portkey.pii, pangea.pii, etc. But the hooks middleware itself will be capable of mutating any other parts of the body and headers.