Add probes support in Triggers eventlistener

[savitaashture]

Changes

• Triggers now support probes setting on EventListener object
• Triggers now have default value for failure-threshold as 3 for both readiness and liveness probes
• Updated doc with the information of supported fields
• Added unit test to cover the field set for kubernetes and custom resources

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• [ ] Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• [ ] Has Tests included if any functionality added or changed
• [ ] Follows the commit message standard
• [ ] Meets the Tekton contributor standards (including functionality, content, code)
• [ ] Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
• [ ] Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings). See some examples of good release notes.
• [ ] Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

Triggers now support probes setting on EventListener object
Triggers now have default value for failure-threshold as 3 for both readiness and liveness probes

[tekton-robot]

The following is the coverage report on the affected files. Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/apis/triggers/v1alpha1/event_listener_validation.go	97.1%	97.3%	0.2
pkg/apis/triggers/v1beta1/event_listener_validation.go	97.2%	97.4%	0.1

[savitaashture]

/hold

[tekton-robot]

The following is the coverage report on the affected files. Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/apis/triggers/v1alpha1/event_listener_validation.go	97.1%	97.2%	0.1
pkg/apis/triggers/v1beta1/event_listener_validation.go	97.2%	97.3%	0.1

[savitaashture]

/lgtm

Also, add the point about default failure threshold in the release note.

Added

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: khrm

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[savitaashture]

/test tekton-triggers-unit-tests