[release-1.19] remove orphaned subscribers from nats jetstream channels

[knative-prow-robot]

This is an automated cherry-pick of #679

Reconclier now can remove non-existing subscriptions.

[codecov]

Codecov Report

❌ Patch coverage is 6.94444% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.14%. Comparing base (5657763) to head (e4a7a19).
⚠️ Report is 1 commits behind head on release-1.19.

Files with missing lines	Patch %	Lines
pkg/channel/jetstream/dispatcher/reconciler.go	7.69%	59 Missing and 1 partial ⚠️
pkg/channel/jetstream/dispatcher/controller.go	0.00%	7 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.19     #686      +/-   ##
================================================
- Coverage         26.59%   26.14%   -0.46%     
================================================
  Files                45       45              
  Lines              2782     2849      +67     
================================================
+ Hits                740      745       +5     
- Misses             1984     2045      +61     
- Partials             58       59       +1     

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[dprotaso]

/override "codecov/patch"
/lgtm
/approve

[knative-prow]

@dprotaso: Overrode contexts on behalf of dprotaso: codecov/patch

Details

In response to this:

/override "codecov/patch"
/lgtm
/approve

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[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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