Wrong OIDC redirect uri path in docs

[andreasntr]

Describe the bug
In docs/AUTHENTICATION.md the default auth redirect uri is reported as https://<your-domain>/api/auth/callback/oidc, which is incorrect.

Expected behavior
OIDC auth redirect uri should instead be https://<your-domain>/api/auth/callback/<provider-name> where provider-name is the value assigned to the OIDC_NAME env.

Example for OIDC_NAME=tinyauth: https://<your-domain>/api/auth/callback/tinyauth

Additional context
Using Docker image ossapps/splitpro:v2.0.3