fix: add feature gate for checking for blank admin/determined password [DET-10197]

[jesse-amano-hpe]

Ticket

DET-10197

Description

Effectively removes service-side checking for blank passwords on default user accounts, by putting it behind a feature switch.

Test Plan

det deploy local commands etc. don't stall for up to 10 minutes

Checklist

• Changes have been manually QA'd
• User-facing API changes need the "User-facing API Change" label.
• Release notes should be added as a separate file under docs/release-notes/.
  See Release Note for details.
• Licenses should be included for new code which was copied and/or modified from any external code.

[netlify]

✅ Deploy Preview for determined-ui canceled.

Name	Link
🔨 Latest commit	f9f8c72
🔍 Latest deploy log	https://app.netlify.com/sites/determined-ui/deploys/6650d0d1f5d70a00082787e0

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.24%. Comparing base (3dfb9ec) to head (f9f8c72).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9425      +/-   ##
==========================================
- Coverage   51.24%   51.24%   -0.01%     
==========================================
  Files         746      746              
  Lines      110663   110663              
  Branches     2777     2777              
==========================================
- Hits        56713    56712       -1     
- Misses      53776    53777       +1     
  Partials      174      174              

Flag	Coverage Δ
backend	34.23% <ø> (-0.05%)	⬇️
harness	64.02% <ø> (ø)
web	44.39% <ø> (ø)

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see 1 file with indirect coverage changes