[e2e] Steps to reduce flakiness in test reporting

[unlikelyzero]

Closes #7441 #6946

Describe your changes:

• adds flake finder PR trigger
• updates circle CI to leverage the custom test runner to shard up Tess and enable test retries

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Is this change backwards compatible? For example, developers won't need to change how they are calling the API or how they've extended core plugins such as Tables or Plots.

Author Checklist

• Changes address original issue?
• Tests included and/or updated with changes?
• Has this been smoke tested?
• Have you associated this PR with a type: label? Note: this is not necessarily the same as the original issue.
• Have you associated a milestone with this PR? Note: leave blank if unsure.
• Is this a breaking change to be called out in the release notes?
• Testing instructions included in associated issue OR is this a dependency/testcase change?

Reviewer Checklist

• Changes appear to address issue?
• Reviewer has tested changes by following the provided instructions?
• Changes appear not to be breaking changes?
• Appropriate automated tests included?
• Code style and in-line documentation are appropriate?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (068ac48) 55.61% compared to head (53213e9) 55.58%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7436      +/-   ##
==========================================
- Coverage   55.61%   55.58%   -0.03%     
==========================================
  Files         668      668              
  Lines       26704    26704              
  Branches     2585     2585              
==========================================
- Hits        14851    14843       -8     
- Misses      11142    11148       +6     
- Partials      711      713       +2     

Flag	Coverage Δ		*Carryforward flag
e2e-full	41.36% <ø> (ø)		Carriedforward from bb27aff
e2e-stable	59.34% <ø> (-0.16%)	⬇️
unit	48.65% <ø> (-0.01%)	⬇️

*This pull request uses carry forward flags. Click here to find out more.

see 3 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 068ac48...53213e9. Read the comment docs.

[ozyx]

LGTM