Node config: add feature flag for http cache headers

What

Adds a config argument for enabling http cache headers.

Why

Since this feature will add slight overhead, it should be opt-in.

Relative (head-n) queries are always changing which creates friction for integrating Octez RPCs with generic Caches as operators needs extra logic/heuristics to know when to invalidate such a response. To get around this, we introduce relevant HTTP Cache headers into the responses of Octez RPCs. The headers to be implemented are max-age and ETag with If-None-Modified. This is an ongoing work with multiple MRs.

This: 1/n
Next: 2/n - !13296 (closed)

How

Update node config and cli

Manually testing the MR

λ /src/bin_node/octez-sandboxed-node.sh 1 --connections 0 --enable-http-cache-headers
...
May 17 14:41:08.592: HTTP cache headers enabled
...

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR