[cherry-pick] disable external redis using acl username auth on release-2.8.0

[MinerYang]

Thank you for contributing to Harbor!

Comprehensive Summary of your change

• introduced by: add external redis username config to support redis6 ACL #18364
• affect version: v2.8.0, v2.8.1, v2.8.2
• impact: distribution performance

Note: distribution configuration (until v2.8.2) only support auth by password

• https://pkg.go.dev/github.com/distribution/distribution/v3/configuration
• https://github.com/distribution/distribution/blob/7c354a4b40feeea21d7eeae4de91c8ff7951e672/registry/handlers/app.go#L530

Issue being fixed

Fixes

Please indicate you've done the following:

• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[codecov]

Codecov Report

Merging #18894 (d61770a) into release-2.8.0 (f8282a5) will increase coverage by 3.13%.
The diff coverage is n/a.

@@                Coverage Diff                @@
##           release-2.8.0   #18894      +/-   ##
=================================================
+ Coverage          67.39%   70.52%   +3.13%     
=================================================
  Files                984      749     -235     
  Lines             107025    93936   -13089     
  Branches            2670        0    -2670     
=================================================
- Hits               72125    66251    -5874     
+ Misses             31017    24100    -6917     
+ Partials            3883     3585     -298     

Flag	Coverage Δ
unittests	70.52% <ø> (+3.13%)	⬆️

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see 240 files with indirect coverage changes

[chlins]

lgtm

[wy65701436]

lgtm

[wy65701436]

don't merge

[MinerYang]

we don't need this, since could bypass this issue by follow this FAQ