Patch fix for issues caused by adding type check in #5906

[aalej]

Description

Type checking reqBody.email and reqBody.password introduced in #5906 caused some issues with the Auth Emulator UI.

Request made by the emulator UI ofter contain a blank values by default. Creating a user via the Emulator UI using phone number will provide a blank email and password string. This will result in the request received by the Auth Emulator to look like:

reqBody: {
  customAttributes: '',
  displayName: '',
  photoUrl: '',
  email: '',
  password: '',
  phoneNumber: '+1230104124',
  ....
} 

Adding type checking of reqBody.email and reqBody.password causes the emulator to always assert a valid email address value. Proposed solution is to remove type check for both reqBody.email and reqBody.password.

To keep the solution in #5906, add a condition to specifically check if reqBody.email is an empty string and a provider is defined (reqBody.email === "" && provider).

Scenarios Tested

Scenario	Prod	Emulator	PR
email="" password=""	Error (auth/invalid-email)	Creates a user with blank identifier and provider	Error (auth/invalid-email)
email="" password="123456"	Error (auth/missing-email)	Error (auth/missing-email)	Error (auth/missing-email)
email="[email protected]" password="123456"	Creates a user with identifier and email provider	Creates a user with identifier and email provider	Creates a user with identifier and email provider

Emulator UI

1. Tested creating a user using only a phone number
2. Tested toggling the verified email toggle in the Auth Emulator UI

[christhompsongoogle]

Nit: add a comment here describing the conditions that we're testing for and why

[aalej]

Added a comment describing the additional condition

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (c552816) 55.02% compared to head (e3552fe) 55.02%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5987   +/-   ##
=======================================
  Coverage   55.02%   55.02%           
=======================================
  Files         339      339           
  Lines       23222    23222           
  Branches     4747     4747           
=======================================
  Hits        12779    12779           
  Misses       9313     9313           
  Partials     1130     1130           

Impacted Files	Coverage Δ
src/emulator/auth/operations.ts	83.42% <100.00%> (ø)

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[aalej]

Closing this PR, changes are fixed in #6127