Adding support for exposures

[ross-whatnot]

As discussed in this issue, adding exposures as a type of evaluable. I believe I've got it plugged into all the right places - tests pass, and I can run rules locally along the lines of the below made-up example:

@rule(severity=Severity.CRITICAL)
def exposures_must_have_owner(exposure: Exposure) -> RuleViolation | None:
    """Exposures may not be owned by Data Team"""
    if exposure.owner["name"] == "Data Team":
        return RuleViolation(
            message=f"Exposure {exposure.name} may not have an owner {exposure.owner['name']}"
        )
    return None

Let me know if I've missed anywhere obvious?

[jochemvandooren]

Sorry for the wait, but looks good! Thanks a lot! 🙌