Set default "Cache-Control" headers in gateway endpoints

[tmm360]

Summary

Some endpoints can have a default Cache-Control header with big values, because expose only immutable values, like for example /bzz. Others instead can have a default Cache-Control: no-cache, because expose dynamic contents, as for /feeds endpoint.

It would be useful to have a default value for these headers, maybe configurable in option.

Motivation

This is useful when using caching systems over the node, without requirement of move cache configuration out of node.

Implementation

Implement a default value for caching, eventually configurable in options.

Drawbacks

Don't see any