All this is doing is wrapping the inner alert details display with a
conditional `{open && ...}`.
This already improves https://github.com/prometheus/prometheus/issues/8548 a
lot for cases where there are many individual firing/pending alert elements
under each alerting rule.
E.g. for a list of 200 rules with ~100 alert elements each, this changed the page
render time from 30 seconds to 1s.
Signed-off-by: Julius Volz <julius.volz@gmail.com>