Allow setting CORS headers

[yiranlus]

This PR allows setting CORS headers:

• Access-Control-Allow-Origin: by setting environment variable TRILIUM_NETWORK_CORS_ALLOW_ORIGIN, or corsAllowOrigin in Network section in config.ini.
• Access-Control-Allow-Methods: by setting environment variable TRILIUM_NETWORK_CORS_ALLOW_METHODS, or corsAllowMethods in Network section in config.ini.
• Access-Control-Allow-Headers: by setting environment variable TRILIUM_NETWORK_CORS_ALLOW_HEADERS, or corsAllowHeaders in Network section in config.ini.

For web browser, due to security reason, it doesn't allow other origins to access Trilium server, e.g., Open WebUI. Modifying these headers will avoid this restriction.

By default, I leave these values empty.

Closes TriliumNext/Trilium#5664

[pano9000]

IMHO, you should also update the config-sample.ini file and add these under the "Network" section as well

[pano9000]

thanks, will do a "live" test this evening (I'm in CEST timezone) and report back :-)

[eliandoran]

Seems fine, even if I didn't test it. We can make adjustments later if needed.