Broadcast: Add codecov to our allowed list

[matejminar]

When adding a new broadcast in the admin panel, the user can include both a URL link and an image link.

There is validation in place for the image link. Due to our CSP (Content Security Policy) rules, if the image link points to a resource on an external server, it will fail and be considered as invalid.

However, our marketing team would like to use images and links from Codecov, as well as arcade GIFs. To allow this, we need to update the allowed list to include https://codecov.io/