Exclude username in password grant error message using OAuth config

[BiyonFernando]

Purpose

• This will add capability to remove the username from Token API Error response with the password grant type
• Related Issues - Remove the username from Token API Error response with the password grant type  wso2/api-manager#3396

Approach

• The below config has to add to deployment.toml to exclude username from error response in password grant token genration.
  [oauth]
exclude_username_in_password_grant_error_message = true
• If the config is not added original behaviour will preserve.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 56.53%. Comparing base (654bc26) to head (7f869f2).
Report is 14 commits behind head on master.

Files with missing lines	Patch %	Lines
...th2/token/handlers/grant/PasswordGrantHandler.java	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2644      +/-   ##
============================================
+ Coverage     56.44%   56.53%   +0.09%     
- Complexity     8193     8213      +20     
============================================
  Files           632      632              
  Lines         46331    46739     +408     
  Branches       8246     8363     +117     
============================================
+ Hits          26151    26425     +274     
- Misses        16465    16601     +136     
+ Partials       3715     3713       -2     

Flag	Coverage Δ
unit	38.84% <50.00%> (+0.18%)	⬆️

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