Add ShowUsernameUnavailability config to self registration

[Yoshani]

Proposed changes in this pull request

Introduce option to handle username existence and non-existence in the same way when account verification is enabled.

Related PRs

• Handle username existence and non-existence similarly wso2/identity-apps#7010
• Update Preference Retrieval Client to get ShowUsernameUnavailability check value wso2/carbon-identity-framework#6046

Related Issues

• Add support to prevent username enumeration in self registration account verification flow wso2/product-is#22101

Checklist (for reviewing)

General

• Is this PR explained thoroughly? All code changes must be accounted for in the PR description.
• Is the PR labeled correctly?

Functionality

• Are all requirements met? Compare implemented functionality with the requirements specification.
• Does the UI work as expected? There should be no Javascript errors in the console; all resources should load. There should be no unexpected errors. Deliberately try to break the feature to find out if there are corner cases that are not handled.

Code

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• Does the PR introduce any inefficient database requests? Use the debug server to check for duplicate requests.
• Are all necessary strings marked for translation? All strings that are exposed to users via the UI must be marked for translation.

Tests

• Are there sufficient test cases? Ensure that all components are tested individually; models, forms, and serializers should be tested in isolation even if a test for a view covers these components.
• If this is a bug fix, are tests for the issue in place? There must be a test case for the bug to ensure the issue won’t regress. Make sure that the tests break without the new code to fix the issue.
• If this is a new feature or a significant change to an existing feature? has the manual testing spreadsheet been updated with instructions for manual testing?

Security

• Confirm this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets.
• Are all UI and API inputs run through forms or serializers?
• Are all external inputs validated and sanitized appropriately?
• Does all branching logic have a default case?
• Does this solution handle outliers and edge cases gracefully?
• Are all external communications secured and restricted to SSL?

Documentation

• Are changes to the UI documented in the platform docs? If this PR introduces new platform site functionality or changes existing ones, the changes should be documented.
• Are changes to the API documented in the API docs? If this PR introduces new API functionality or changes existing ones, the changes must be documented.
• Are reusable components documented? If this PR introduces components that are relevant to other developers (for instance a mixin for a view or a generic form) they should be documented in the Wiki.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 36.41%. Comparing base (a4ed43e) to head (957d049).
Report is 161 commits behind head on master.

Files with missing lines	Patch %	Lines
...recovery/connector/SelfRegistrationConfigImpl.java	90.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master     #870       +/-   ##
=============================================
+ Coverage     22.15%   36.41%   +14.26%     
- Complexity      915     1451      +536     
=============================================
  Files           267      267               
  Lines         15472    15800      +328     
  Branches       2092     2183       +91     
=============================================
+ Hits           3428     5754     +2326     
+ Misses        11590     9330     -2260     
- Partials        454      716      +262     

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[Yoshani]

UI:

[jenkins-is-staging]

PR builder started
Link: https://github.com/wso2/product-is/actions/runs/11451688156

[jenkins-is-staging]

PR builder completed
Link: https://github.com/wso2/product-is/actions/runs/11451688156
Status: failure

[Yoshani]

Integration test failure will be fixed with wso2/product-is#21447 once this is bumped into prod-is.