Add webhook notification type

[fg91]

Tracking issue

https://github.com/flyteorg/flyte/issues/

Why are the changes needed?

What changes were proposed in this pull request?

How was this patch tested?

Setup process

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Check all the applicable boxes

• [ ] I updated the documentation accordingly.
• [ ] All new and existing tests passed.
• [ ] All commits are signed-off.

Related PRs

Docs link

[codecov[bot]]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (6cd0a60) 85.98% compared to head (a40e9b2) 50.86%. Report is 11 commits behind head on master.

Files	Patch %	Lines
flytekit/models/common.py	61.29%	12 Missing :warning:
flytekit/core/notification.py	50.00%	2 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2060       +/-   ##
===========================================
- Coverage   85.98%   50.86%   -35.12%     
===========================================
  Files         308      175      -133     
  Lines       22946    16955     -5991     
  Branches     3468     3486       +18     
===========================================
- Hits        19731     8625    -11106     
- Misses       2615     7907     +5292     
+ Partials      600      423      -177     

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