fix: resend events only for retryable errors

[chetan-rns]

What does this PR do / why we need it:

• Check if the error is retryable/transient.
• Don't send an ACK for retryable errors so that the principal can resend events.

Which issue(s) this PR fixes:

Fixes #243

How to test changes / Special notes to the reviewer:

Checklist

• Documentation update is required by this PR (and has been updated) OR no documentation update is required.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 68 lines in your changes missing coverage. Please review.

Project coverage is 46.79%. Comparing base (d950aaa) to head (aa500c4).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/kube/client.go	0.00%	50 Missing ⚠️
agent/connection.go	0.00%	12 Missing ⚠️
principal/event.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #254      +/-   ##
==========================================
- Coverage   47.21%   46.79%   -0.43%     
==========================================
  Files          55       55              
  Lines        4882     4939      +57     
==========================================
+ Hits         2305     2311       +6     
- Misses       2401     2451      +50     
- Partials      176      177       +1     

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[jannfis]

LGTM! Thanks.