Warn when custom headers are omitted

[peterpeterparker]

Motivation

The custom headers defined by the developers are applied unless they conflicts with security headers - that can or not be disabled.

This can be misleading for the devs, as they have no direct ways to figure this out. The documentation kind of explains it and the source code, well, is written in Rust and we should not expect dev to read the source code of the Satellite.

Long story short, we should print a warning when a custom header will be omitted.

Discussed with @FlavioInacta

Example

storage: {
      headers: [
        {
          source: "/storybook/**",
          headers: [["X-Frame-Options", "SAMEORIGIN"]],
        },
      ],
    },

The default iframe config overwrites the above.