add periodic e2e tests that post to slack on failure

[vaikas]

Proposed Changes

• Run periodic (every 4 hours) kind e2e tests. On failure, post to slack.

Release Note

- 🎁 Add new feature
Run kind e2e tests every 4 hours on Github actions.

Docs

[slinkydeveloper]

/lgtm
/approve

Cool! This will hopefully help us figure out the flakyness issues more easily

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: slinkydeveloper, vaikas

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• OWNERS [slinkydeveloper,vaikas]

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[codecov]

Codecov Report

Merging #4412 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4412   +/-   ##
=======================================
  Coverage   81.09%   81.09%           
=======================================
  Files         281      281           
  Lines        7961     7961           
=======================================
  Hits         6456     6456           
  Misses       1119     1119           
  Partials      386      386           

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