### What?
Updates the tenant selector displayed in the sidebar when a new tenant
is created.
### Why?
Currently when using the multi-tenant plugin and creating a new tenant
doc, the tenant selector dropdown does not display the new tenant as an
option until the page gets refreshed.
### How?
Extends the `WatchTenantCollection` helper to check if the tenant `id`
from the current doc exists, if the tenant is new it manually calls
`updateTenants`. The `updateTenants` function previously only adjusted
the title on existing tenants, this has been updated to add a new tenant
as an option when it doesn't exist.
#### Reported by client
c76d83985d