[Security] Improve default security

Problem/Motivation

The default security delivered by our installation profile can be greatly improved to provide a better scoring on tools like sonarQube or Mozilla Observatory.

Proposed resolution

Please review the following security workshop to implement most of its best practices (mostly the HTTP security headers) : https://gitlab.com/nicoloye/drupal-security-101/-/blob/main/README.md?re...

The conference slides are available at the end of the file.

Remaining tasks

• Analyze the workshop
• List the practices to be integrated
• Implement the practices