feat: move cache control policy to standalone config section

[df-wg]

In #1155, we added in support for having a restrictive cache control policy, as part of the header rules. This pulls out the cache control configuration into a standalone section of the configuration, for clarity and extensibility.

It can now be configured like:

cache_control_policy:
  enabled: true
  value: "max-age=180, public"
  subgraphs:
    - name: "products"
      value: "max-age=60, public"

Additionally, in #1196 we had created a set header operation. This PR adds tests to validate that using the set header operation, we can, if necessary, override the cache control restrictions, as a 'break-glass' measure.

Motivation and Context

TODO

• Tests or benchmark included
• Documentation is changed or added on https://app.gitbook.com/
• PR title must follow conventional-commit-standard

[StarpTech]

LGTM