Refactor GoCD Slack feed handler to handle failures gracefully

[IanWoodard]

This aims to better handle potential failures, especially now that we have quite a few deploy feeds.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.25%. Comparing base (c89c067) to head (d003021).
⚠️ Report is 130 commits behind head on main.

Files with missing lines	Patch %	Lines
src/brain/gocdSlackFeeds/index.ts	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #776      +/-   ##
==========================================
- Coverage   86.26%   86.25%   -0.02%     
==========================================
  Files         116      116              
  Lines        3306     3310       +4     
  Branches      664      665       +1     
==========================================
+ Hits         2852     2855       +3     
- Misses        440      441       +1     
  Partials       14       14              

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