Pushover emergency priority

Would be great to be allowed to set a "priority" value.

And if "priority" is set to 2, we want to set "retry" and "expire" for the recurring messages until acknowledgement.

No file, test, or entry point is named. Start by locating the Pushover notification integration and its handling of message priority; then determine how priority 2 should apply retry and expire values to recurring messages until acknowledgement. Done means callers can set priority and priority 2 produces the requested recurring-message behavior.

Written by the indexing model from the issue text.