Beta uplift nag template should suggest asking for release uplift if we're in RC week (and mention that we're in RC week)

As per summary. Example: https://bugzilla.mozilla.org/show_bug.cgi?id=1992036#c5 

At this point (Tue in RC week), it's too late for beta uplifts. Release uplifts would still work but of course the bar is quite high...

The comment should be clear about both of those (and definitely not suggest asking for beta uplift)