Refactor NGINX config uploads

[alessfg]

Proposed changes

• Rename upload related variables:
  • Rename the nginx_config_snippet_upload_* parameters to nginx_config_upload_* (check defaults/main/upload.yml for an example).
  • Rename the nginx_config_html_upload_* parameters to nginx_config_upload_html_*.
  • Rename the nginx_config_ssl_upload_* parameters to nginx_config_upload_ssl_*.
• Tweak the nginx_config_html_upload and nginx_config_ssl_upload parameters to now use a list instead of a single src and dest value (check defaults/main/upload.yml for an example).

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have added Molecule tests that prove my fix is effective or that my feature works
• I have checked that all Molecule tests pass after adding my changes
• I have updated any relevant documentation (defaults/main/*.yml, README.md and CHANGELOG.md)