nginx: deprecated OIDC callback path prefix used

[hauau]

As per synapse 1.27.0rc1 open id connect callback URI changed to /_synapse/client/oidc from /_synapse/oidc:

https://github.com/matrix-org/synapse/blob/develop/CHANGES.md#synapse-1270rc1-2021-02-02
matrix-org/synapse#9288

Currently this playbook uses separate /_synapse/oidc path location forwarding flag:
matrix_nginx_proxy_proxy_matrix_client_api_forwarded_location_synapse_oidc_api_enabled

Now this can be handled with other existing flag:
matrix_nginx_proxy_proxy_matrix_client_api_forwarded_location_synapse_client_api_enabled

That means if your client location prefix disabled your requests won't be properly forwarded and oidc setting won't do anything useful.