OIDC: Add cookie path configuration to SecurityPolicy

*Description*:
>Describe the desired behavior, what scenario it enables and how it
would be used.

It would be useful to be able to set the cookie path for the OIDC session and CSRF cookies so that unique sessions/clients can be supported with path-based routing. This is functionality supported by many other OAuth2/OIDC proxies. The main use case is for applications which operate as gateways and may have modular frontend shells serving content from backends in different logical boundaries and therefore operate with different OAuth2 clients.