Resolve "Only show the call disclaimer once"

What does this MR do?

The popup will only be shown the first time the user enters the room. A cookie is stored permanently when they access it for the first time so we can verify this for the future.

Does this MR meet the acceptance criteria?

• I have added tests to validate the new functionality.
• I have updated the documentation accordingly.
• I have added translations for all new client-side text.

Closes #124 (closed) Closes #142 (closed)