I have some concerns with this approach. They might not be valid but I want to put them on table nevertheless:
1. How is the authentication of tenants handled? From what I understand, these will be special administrative tenants and I believe there should be some kind of authentication attached to them. Otherwise, a non-administrative tenant, would be able to submit batched multi-tenant metrics by just knowing the tenantID.
2. If someone submits metrics using the admin tenantId and does not include the `X-Multitenant` header, the request body will be parsed using non-scoped `JSONMetric` class and metrics will be improperly inserted for the admin tenantID, which is wrong. This leads me to think there should be some validation before inserting metrics via this admin tenantId, like we should not allow anyone to submit metrics without attached tenantId and without the `X-MultiTenant` header via this tenantId.
3. I think we should not infiltrate this handler for just < 1% of admin tenants and this should be handled in a separate code path may be on a separate endpoint? We can probably discuss how we want it handled, but I think this is beyond the scope of this PR and we should probably handle this in a separate PR?