:bug: `set_rev_reg_state` in revocation_anoncreds is unimplemented

[ff137]

Here is the set_rev_reg_state method in revocation_anoncreds:

async def set_rev_reg_state(request: web.BaseRequest):
    """Request handler to set a revocation registry state manually.

    Args:
        request: aiohttp request object

    Returns:
        The revocation registry record, updated

    """
    context: AdminRequestContext = request["context"]
    profile = context.profile

    is_not_anoncreds_profile_raise_web_exception(profile)

    rev_reg_id = request.match_info["rev_reg_id"]
    state = request.query.get("state")

    try:
        revocation = AnonCredsRevocation(profile)
        rev_reg_def = await revocation.set_rev_reg_state(rev_reg_id, state)
        if rev_reg_def is None:
            raise web.HTTPNotFound(reason="No rev reg def found")

    except AnonCredsIssuerError as e:
        raise web.HTTPInternalServerError(reason=str(e)) from e

    rev_reg = await _get_issuer_rev_reg_record(profile, rev_reg_id)
    return web.json_response({"result": rev_reg.serialize()})

Note:

        rev_reg_def = await revocation.set_rev_reg_state(rev_reg_id, state)
        if rev_reg_def is None:
            raise web.HTTPNotFound(reason="No rev reg def found")

Let's look at that revocation.set_rev_reg_state method:

    async def set_rev_reg_state(self, rev_reg_id, state):
        """Update Revocation Registry state."""
        pass

Oh. it's not implemented, and returns None.

So, HTTPNotFound(reason="No rev reg def found") will always be raised.

Either this should be implemented or removed