Multiple Content-Security-Policy headers

[4170R]

Is it possible to add multiple Content-Security-Policy headers with this package?
Its's necessary for some specifications, but I don't know how do that.

Examples of use: https://content-security-policy.com/examples/multiple-csp-headers/

[freekmurze]

Currently I don't have time to implement this, but I'd happy merge a well tested and documented PR.