[Known issue][Detection Engine] Exception item comment validation on newline chars

[yctercero]

Summary

I wasn't sure if this required a docs issue as it would get picked up by release notes, but will create just in case.

Issue: elastic/kibana#201820
PR: elastic/kibana#202063
Workaround: elastic/kibana#201820 (comment)

Fix slated for 8.16.2

Bug Summary

After upgrading a deployment from any version below 8.16.0 to 8.16+, any rule exceptions with comments containing newline char \n will throw a 500 in the exception items _find api, like when trying to view the exceptions in the rule details page.