fix(discord): Handle case where issue does not exist

[spalmurray]

• Gracefully handle case where issue does not exist
• Add message param to DiscordInteractionHandlerError
• Add test

FIXES SENTRY-150T

[codecov]

Codecov Report

Merging #55161 (57dfe5b) into master (2e10de6) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #55161      +/-   ##
==========================================
- Coverage   79.95%   79.95%   -0.01%     
==========================================
  Files        5034     5034              
  Lines      214524   214539      +15     
  Branches    36439    36440       +1     
==========================================
+ Hits       171514   171525      +11     
- Misses      37743    37747       +4     
  Partials     5267     5267              

Files Changed	Coverage Δ
src/sentry/integrations/discord/webhooks/base.py	100.00% <100.00%> (ø)
...rc/sentry/integrations/discord/webhooks/handler.py	100.00% <100.00%> (ø)
...integrations/discord/webhooks/message_component.py	98.38% <100.00%> (+0.05%)	⬆️

... and 5 files with indirect coverage changes