docs: Add technique for ConfigMap change detection in Rollout

[OpenGuidou]

As it seems there are several questions around the topic, adding it in the doc.

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.

[github-actions]

Go Published Test Results

2 160 tests   2 160 ✅  2m 53s ⏱️
  119 suites      0 💤
    1 files        0 ❌

Results for commit 23e6bb5.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.85%. Comparing base (8405f2e) to head (23e6bb5).
Report is 83 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3515      +/-   ##
==========================================
+ Coverage   81.83%   82.85%   +1.01%     
==========================================
  Files         135      135              
  Lines       20688    17142    -3546     
==========================================
- Hits        16931    14203    -2728     
+ Misses       2883     2046     -837     
- Partials      874      893      +19     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[github-actions]

E2E Tests Published Test Results

  4 files    4 suites   3h 25m 13s ⏱️
110 tests  97 ✅  6 💤  7 ❌
452 runs  416 ✅ 24 💤 12 ❌

For more details on these failures, see this check.

Results for commit 23e6bb5.

[zachaller]

thanks for the docs!