feat: generic webhook receiver

[fuskovic]

Closes: https://github.com/akuity/kargo/issues/4486

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[codecov[bot]]

Codecov Report

:x: Patch coverage is 78.18792% with 65 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 56.30%. Comparing base (7e94944) to head (6880010). :warning: Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/webhook/kubernetes/external/validation.go	0.00%	33 Missing :warning:
pkg/webhook/external/generic.go	81.81%	17 Missing and 1 partial :warning:
pkg/api/warehouse.go	0.00%	8 Missing :warning:
pkg/webhook/external/generic_list_options.go	96.15%	2 Missing and 2 partials :warning:
pkg/webhook/external/generic_actions.go	93.75%	1 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5305      +/-   ##
==========================================
+ Coverage   55.99%   56.30%   +0.31%     
==========================================
  Files         409      414       +5     
  Lines       29992    30347     +355     
==========================================
+ Hits        16793    17087     +294     
- Misses      12227    12282      +55     
- Partials      972      978       +6     

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