Add configuration for CORS policy

[polymutex]

I am trying to set up Helios as backend for a locally-running Eternal Safe frontend. However, it runs into CORS issues, because the Eternal Safe frontend is running on a different localhost port from the one that Helios is running as.

Ideally, Helios would have a flag like --allow-cors-origin=http://localhost:someport or --allow-cors-origin=* and return the right headers when queried about CORS policy for such origins.

Ideally, a default allowing localhost origins may be useful to make local use easier out of the box.

[ncitron]

Good idea. Will work on this soon.

[SakshiShah29]

Could you assign this to me? I'd like to work on it.