fix: make some admin billing fields optional

[maze-runnar]

Fixes #5106

Checklist

• I have read the Contribution & Best practices Guide.
• My branch is up-to-date with the Upstream development branch.
• The acceptance, integration, unit tests and linter pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

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[iamareebjamal]

You still need to verify the validity of the phone number, but make it optional

[codecov]

Codecov Report

Merging #5114 into development will decrease coverage by 0.03%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development    #5114      +/-   ##
===============================================
- Coverage        22.83%   22.80%   -0.04%     
===============================================
  Files              489      489              
  Lines             5162     5169       +7     
  Branches            35       35              
===============================================
  Hits              1179     1179              
- Misses            3978     3985       +7     
  Partials             5        5              

Impacted Files	Coverage Δ
app/components/forms/admin/settings/billing.js	0.00% <ø> (ø)
app/mixins/event-wizard.js	0.98% <0.00%> (-0.08%)	⬇️

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[iamareebjamal]

This was below phone rule. So please move it there. Try to make least amount of diff as possible to make it easy to review