Custom styles to custom feedback

[Arthurk12]

Description

Currently, the custom feedback uses the same css variables as the html5 client but the colors are not applied because it is a separate application/page. So we should think in a way to apply the custom styles to it. I see 2 approaches:

1. The html5 client would send the custom styles url to the custom feedback as a query parameter, as it is done with the meetingId, userId and exit reason;
2. There should be a configuration file or something like that in the project that allows defining custom colors for the UI.