Add warm-up

Preliminary testing shows that cold Jira Cloud nodes show very poor performance when they come up and that this fades, generally very quickly if people are active on it. This suggests that the penalty is due to classloading and just-in-time compilation and that “warming” the converters will help avoid the problem.

The ask here is to add an out-of-the-box warmer that will try to hit all major code paths in the conversion code.