chore: Clarify log entry requirements in bug report form

[joshtrichards]

Summary

• We don't want (or need) to the entire log file
  • GitHub will reject it anyhow
  • Reporters get annoyed/confused
  • Wading through days/weeks/months/years of log entries isn't conducive to efficient triaging / bug analysis :)
• Also adjust automatic rendering to json (note: I think the automated adding of codeblocks via Issue templates automatically is broken right now on GitHub; I've noticed more Issues coming in that are missing codeblock markers but that's a GH bug... I don't think it's us).

TODO

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[szaimen]

LGTM