Sanitize Reaper secrets names to gracefully handle cluster name overrides

[adejanovski]

What this PR does:
What the title says, plus modify single dc reaper e2e tests to use an override.
Also renames the CreateSingleReaper subtest to CreateSingleReaperNoStargate, because running CreateSingleReaper  would also run CreateSingleReaperWStargateAndHTTP as it begins with the same string.

Which issue(s) this PR fixes:
Fixes #1002

Checklist

• Changes manually tested
• Automated Tests added/updated
• Documentation added/updated
• CHANGELOG.md updated (not required for documentation PRs)
• CLA Signed: DataStax CLA

[sonarqubecloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
14.3% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (dfcd0bf) 57.05% compared to head (d5dae29) 56.99%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1176      +/-   ##
==========================================
- Coverage   57.05%   56.99%   -0.06%     
==========================================
  Files         101      101              
  Lines       10437    10437              
==========================================
- Hits         5955     5949       -6     
- Misses       3961     3965       +4     
- Partials      521      523       +2     

Files	Coverage Δ
pkg/reaper/secrets.go	4.34% <50.00%> (ø)

... and 2 files with indirect coverage changes

[adejanovski]

Thanks for the quick review @emerkle826 !