Add "Euthanized" to icarDeathMethod

[cookeac]

Discussed in #513

^{Originally posted by jdoemel February 1, 2025}
Could euthanized be added as a deathMethod to the GET and POST deaths endpoints

I agree, euthanised/euthanized would be a method of death, not a reason.
I'll add this as an issue for discussion with the group. I think most people have used "Perished" which implies died for other than an accident, but doesn't distinguish between animals which died of sickness vs. those that had to be euthanised for sickness.