Extend Cache Policy to support more configuration parameters

[thresheek]

Is your feature request related to a problem? Please describe.
Currently, on 5.2.0, Cache Policy doesnt allow users to specify inactivity and use_temp_path parameters as available for proxy_cache_path directive. This means that users cant set the inactive cache lifetime and are forced to spend disk IO on moving the cache files (e.g. when using a StatefulSet and a separate volume).

Those are the options that were specifically asked by the customers.

Additionally, it's not possible to configure:

• anything cache manager related in proxy_cache_path - max_size, min_free, manager_* which are crucial to maintain the filesystem usage for caches

• loader_* is less widely used, but sometimes tuning can be beneficial in the scenarios where NGINX is restarted and needs to prime the cache info

• proxy_cache_key which would allow users to redefine the caching keys for the cache items

• proxy_cache_use_stale and proxy_cache_revalidate are useful to minimize the impact on backends when updating the expired cached items

• proxy_no_cache and proxy_cache_bypass would allow to bypass the caching for specific requests

• proxy_cache_lock* directives are useful for highly loaded services, eliminating the pressure on backends

Describe the solution you'd like
A support for aforementioned items in the Cache Policy

Describe alternatives you've considered
Snippets can still be used to implement the desired functionality.

[thresheek]

I've got a confirmation from a customer that they use the following directives:

proxy_cache
proxy_cache_background_update
proxy_cache_key
proxy_cache_lock
proxy_cache_min_uses
proxy_cache_path
proxy_cache_revalidate
proxy_cache_use_stale
proxy_ignore_headers

They confirmed they use inactive and use_temp_path in proxy_cache_path, and redefine proxy_cache_key using a mix of nginx-provided built-in variables and variables set up by map, too.