Inter-catalyst connections blocked due to CORS

Steps to reproduce:
1) Upload a video file to a DCL scene.
2) Cast the video to a texture via SDK.
3) Enter the scene in a modern browser.

Expected outcome:
The video loads and plays on the texture (works as expected via the desktop app).

Actual outcome:
No video. In the browser logs can be seen, e.g. in Firefox:
```
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://peer.melonwave.com/content//contents/bafybeidrsigw4lxzsyyrwzmwuiz5obcofxscvczhbqrzri3skplfnq4bw4. (Reason: CORS request did not succeed). Status code: (null).
```

Work-around:
* Join realms other than `Main`. Eventually the video loads, then appears to be cached, and available when returning to `Main`.
OR
* Use an add-on or an extension which appends reparative CORS headers.

Notes:
This is only one of the possible `Steps to reproduce`.
Many other such messages can be seen in the console:
`Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://peer.dclnodes.io/stats/parcels. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 404.`
`Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://rpc.decentraland.org/polygon. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 500.`
`Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://social.decentraland.org/_matrix/client/r0/sync?filter=0&timeout=30000&[...]. (Reason: CORS request did not succeed). Status code: (null).`
etc