Rework Caddyfile

[inetol]

This PR completely reworks the Caddy config file to solve several inconveniences that are not worth having them in separate PRs, the changes are these...

• Try to protect the user data (query searches, IPs and headers) logged on Caddy if there is an error with the upstream response (or Caddy itself).
• Overwrite the Cache-Control and Content-Security-Policy headers if its matcher token matches rather than doing the comparison twice in a row.
• Prefer to set the ENV defaults directly in the Caddyfile.
• Modified the Strict-Transport-Security header to not include all subdomains in the HSTS policy nor mark the latter to enter the HSTS preload list.
• Modified the Permissions-Policy header to remove useless features.
• Remove the encode directive, otherwise Caddy will not passthrough the precompressed files served by uWSGI.
• Remove the X-XSS-Protection and Feature-Policy headers following the standards recommendations and evaluating the possible impact with older clients.
• Other minor structure and format changes.

All changes have been tested and validated without requiring major changes for users.