add landing configuration for Nginx reverse proxy

[runleveldev]

This pull request introduces a new Nginx server configuration for opensource.mieweb.org, enabling secure HTTPS access with modern TLS, HTTP/2, and HTTP/3 support, and proxying requests to a backend service. The configuration also includes enhanced security headers and optimizations for SSL performance.

New Nginx reverse proxy configuration:

• Added a new server block in landing.conf to listen on port 443 with SSL, HTTP/2, and HTTP/3 (QUIC) enabled for opensource.mieweb.org.
• Configured SSL certificates, modern TLS protocols/ciphers, session optimizations, and OCSP stapling for improved security and performance.
• Added security headers such as Strict-Transport-Security, X-Frame-Options, X-Content-Type-Options, and X-XSS-Protection to enhance browser security.
• Set up a reverse proxy to forward requests to the backend at 10.15.0.4:2998, including support for WebSockets, appropriate proxy headers, timeouts, and large file uploads.

[cmyers-mieweb]

lgtm