disable external redis using acl username auth

[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 #18893 (8c46d98) into main (1efe944) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main   #18893   +/-   ##
=======================================
  Coverage   67.40%   67.40%           
=======================================
  Files         981      981           
  Lines      107194   107194           
  Branches     2698     2698           
=======================================
+ Hits        72250    72256    +6     
+ Misses      31059    31055    -4     
+ Partials     3885     3883    -2     

Flag	Coverage Δ
unittests	67.40% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 8 files with indirect coverage changes

[wy65701436]

LGTM

[chlins]

lgtm

[wy65701436]

don't merge

[MinerYang]

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