add hostname to default error boundary message (#75151)
Since it's possible to deploy an application that triggers our default
exception handling, we should ensure the error text is personalized to
the host application to avoid any potential incorrect canonicalization
by search engines for containing duplicate content.
[slack
context](https://vercel.slack.com/archives/C01A2M9R8RZ/p1737475474278219?thread_ts=1737385764.035219&cid=C01A2M9R8RZ)
