Add EventTransform API types

[pierDipi]

Event transformations are essential to connect different systems, with the EventTransform we will support this use cases where a generic and declarative event transformation can be used and we would not require custom code to do that.

The API can be used in different places, between a source/webhook and a broker, between a broker and a sink or even leverage the built-in Trigger transformation feature with response.

source or webhook -> transform -> broker

trigger -> transform -> sink or webhook

broker -> trigger -> (request)  -> transform
broker <- trigger <- (response) <-

Related to:

• Trigger: add customized fields into cloudevent extension after the event passes a trigger filter #7704
• ApiServerSource: add optional selection criteria to ceOverride.extensions based on fields in the cloudevent #8001

We would also solve use cases like this https://cloud-native.slack.com/archives/C06AH2C3K8B/p1731786548587349 where a sink is OpenAI compatible LLM endpoint without writing custom code.

First commit is the main commit, rest is codegen and fixes

Proposed Changes

• Add EventTransform API
• Support for JSON transformations with JSONata expressions: Add Jsonata transformation server knative-extensions/eventing-integrations#62

Pre-review Checklist

• At least 80% unit test coverage
• E2E tests for any new behavior
• Docs PR for any user-facing impact
• Spec PR for any new API feature
• Conformance test for any change to the spec

Release Note

Add EventTransform API types.

Docs

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 90 lines in your changes missing coverage. Please review.

Project coverage is 63.92%. Comparing base (4a6e7d2) to head (90e86eb).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...apis/eventing/v1alpha1/eventtransform_lifecycle.go	50.00%	39 Missing and 4 partials ⚠️
...pis/eventing/v1alpha1/eventtransform_validation.go	0.00%	41 Missing ⚠️
pkg/apis/eventing/v1alpha1/eventtransform_types.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8447      +/-   ##
==========================================
- Coverage   64.10%   63.92%   -0.18%     
==========================================
  Files         388      391       +3     
  Lines       23363    23498     +135     
==========================================
+ Hits        14976    15021      +45     
- Misses       7591     7677      +86     
- Partials      796      800       +4     

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[pierDipi]

/test unit-tests

[pierDipi]

/test reconciler-tests

[pierDipi]

/test reconciler-tests

[matzew]

I think this is not the end of the world, if reflected broken expressions via "runtime errors" propagated to the status of the thing

[matzew]

has the $ a special meaning?

[pierDipi]

yes, $ is basically the input / root node

{"hello": "Matthias"} with transformation {"data": $ } results in {"data": {"hello": "Matthias"} }

See for example: https://try.jsonata.org/quwrKXzni

For the same input:

{"data": $.hello, "data2": hello, "full": $ }

returns

{
  "data": "Matthias",
  "data2": "Matthias",
  "full": {
    "hello": "Matthias"
  }
}

[matzew]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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