test: add unit tests for maxSurge=0, replicas=1

[agaudreault]

When testing rollouts with 1 replica and maxSurge=0, the observed behavior was different than the one documented. No unit tests were covering the case.

This adds unit tests, updates documentation based on current behavior and tries to clarify the unit tests by using the same terminology amongst them.

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
• The title of the PR is (a) conventional with a list of types and scopes found here, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234".
• I've signed my commits with DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My builds are green. Try syncing with master if they are not.
• My organization is added to USERS.md.

[sonarcloud]

Quality Gate passed

Issues
0 New issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[github-actions]

Go Published Test Results

2 127 tests   2 127 ✅  2m 50s ⏱️
  118 suites      0 💤
    1 files        0 ❌

Results for commit 3acd985.

[codecov]

Codecov Report

Attention: 69 lines in your changes are missing coverage. Please review.

Comparison is base (8405f2e) 81.83% compared to head (3acd985) 82.98%.
Report is 15 commits behind head on master.

Files	Patch %	Lines
controller/controller.go	21.68%	61 Missing and 4 partials ⚠️
utils/record/record.go	50.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3375      +/-   ##
==========================================
+ Coverage   81.83%   82.98%   +1.14%     
==========================================
  Files         135      135              
  Lines       20688    16854    -3834     
==========================================
- Hits        16931    13986    -2945     
+ Misses       2883     1996     -887     
+ Partials      874      872       -2     

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[github-actions]

E2E Tests Published Test Results

  4 files    4 suites   3h 44m 35s ⏱️
107 tests  97 ✅  6 💤  4 ❌
438 runs  404 ✅ 24 💤 10 ❌

For more details on these failures, see this check.

Results for commit 3acd985.