Consolidate test utility functions into top level package

[dereknola]

Proposed Changes

• Consolidate relevant "client-go" type helper functions into a single package for use across Integration, Docker, and E2E tests. Docker and Integration were already directly using their respective client-go functions, E2E reqiured more work (as those relied on kubectl calls on the host, not client-go API calls).
• Add missing Context levels in several E2E tests.
• Convert several E2E test functions into methods, consolidate common variables into Test Config struct. This brings E2E closer to how the docker tests are constructed, enabling easier "translation" between a docker or a E2E test.

Types of Changes

Testing

Verification

CI still green for all tests.

Testing

Testing all the way down

Linked Issues

#11710

User-Facing Change

Further Comments

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 101 lines in your changes missing coverage. Please review.

Project coverage is 47.41%. Comparing base (1666b5c) to head (2d1c463).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
tests/client.go	0.00%	101 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11711      +/-   ##
==========================================
- Coverage   47.65%   47.41%   -0.25%     
==========================================
  Files         185      186       +1     
  Lines       19353    19454     +101     
==========================================
+ Hits         9223     9224       +1     
- Misses       8797     8896      +99     
- Partials     1333     1334       +1     

Flag	Coverage Δ
e2etests	40.38% <ø> (ø)
inttests	35.06% <ø> (+0.04%)	⬆️
unittests	16.95% <0.00%> (-0.09%)	⬇️

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