Add util method to get root domain

[Yoshani]

Proposed changes in this pull request

Adds a util method to get root domain of a given domain.

When should this PR be merged

Upon review

Related issues

• Issue Auto login does not work when self registering in a custom domain configured org product-is#21135

Related PRs

• Set root domain of custom domain for ALOR cookie identity-apps#6904

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

• Do you fully understand the introduced changes to the code? If not ask for clarification, it might uncover ways to solve a problem in a more elegant and efficient way.
• 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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 22.42%. Comparing base (740471e) to head (8163d36).
Report is 39 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5944      +/-   ##
============================================
+ Coverage     22.40%   22.42%   +0.02%     
- Complexity     5985     5994       +9     
============================================
  Files          1561     1561              
  Lines         99212    99248      +36     
  Branches      15183    15187       +4     
============================================
+ Hits          22226    22259      +33     
  Misses        73777    73777              
- Partials       3209     3212       +3     

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