Add help page section on rate cap removal

[RichardTaylor]

A starting point could be the message shown to users who hit the rate cap

https://github.com/mysociety/alaveteli/blob/a27a28ef18e8c23f2757272d0629ec0c2f705799/app/views/user/rate_limited.html.erb

The reason for this is we want to remove restrictions on those making good use of the service, we want to encourage and enable requests to be made in public via the service.

Related:

• https://github.com/mysociety/alaveteli/issues/7083
• https://github.com/mysociety/alaveteli/issues/6789

[garethrees]

What do we want to say? Could it just be integrated into the page itself?