APIM - Documentation for tenants and sharding tags

[mouligno]

What is it and how we can use them ?

a sharding tag is used to define which APIs will be deployed to which Gateway, but a tenant defines which backend endpoints an API should route to based on it's gateway's tenant configuration

We should have some real life example for CI/CD purrposes for example

Can be access via EL : {#node.tenant}

[plsstephenson]

This needs adding as a section of the Administration Guide, along with all Organization Settings.