Global cookie_name_prefix is incompatible with redis

For cookie_name_prefix, the authservice configuration documentation states:

Also needed when an Authservice is configured with multiple oidc filters (across multiple chains), each sharing a Redis server for their session storage, to avoid having those oidc filters read/write the same sessions in Redis.

This means that if using Redis, the cookie_name_prefix must be unique for each chain.

This means that the concept of a globally configured cookie_name_prefix doesn't make much sense, but this chart currently allows configuring global.cookie_name_prefix

Users could just configure each chain manually to provide a unique cookie_name_prefix, except that the BB generated chains are using the global cookie_name_prefix because none is provided in their chains:
https://repo1.dso.mil/platform-one/big-bang/bigbang/-/blob/b1e2c632ce724e01d1ae46752ac0c58c4c476cf7/chart/templates/authservice/values.yaml#L50-66