Make SecretSpec field of consumers Auth omitempty

[mgencur]

This will prevent writing SecretSpec with null value and the webhook will rather omit the element.

 spec:
        auth:
          SecretSpec: null

Having the element there with null value can also caus problems during downgrades when the element was not there yet (it's a few versions back though)

Proposed Changes

Release Note

Docs

[codecov]

Codecov Report

Merging #3286 (5cf465d) into main (842eb1c) will increase coverage by 3.23%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main    #3286      +/-   ##
============================================
+ Coverage     58.56%   61.80%   +3.23%     
- Complexity        0      765     +765     
============================================
  Files            91      181      +90     
  Lines          9159    12220    +3061     
  Branches          0      266     +266     
============================================
+ Hits           5364     7552    +2188     
- Misses         3375     4080     +705     
- Partials        420      588     +168     

Flag	Coverage Δ
java-unittests	71.57% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
...nternals/kafka/eventing/v1alpha1/consumer_types.go	72.97% <ø> (ø)

... and 91 files with indirect coverage changes

[matzew]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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