Leverage Mozilla Observatory to improve security

[rgreinho]

Issue Type

• Bug report
• Feature request

Current Behavior

Using https://observatory.mozilla.org/analyze/viz.scrapd.org, we currently only score a "D" as we are missing several important headers.

Expected Behavior

The goal would be to follow the Mozilla recommendations and get an "A".

[rgreinho]

Using helmet seems to be a good approach to implement the security headers.

[rgreinho]

Mozilla observatory Report

[rgreinho]

Re-opening this issues as the changes do not work with the static export.

Refer to this PR: vercel/next.js#4943 for some pointers.