Add config to disable the org branding self signup URL

[brionmario]

Purpose

Describe the problem, feature, improvement or the change introduces by the PR briefly. Add screenshots/GIFs if UI/UX changes are introduced. Remove this placeholder when you're editing.

Related Issues

• Issue #1 or (None)

Related PRs

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Checklist

• e2e cypress tests locally verified.
• Manual test round performed and verified.
• UX/UI review done on the final implementation.
• Documentation provided. (Add links if there are any)
• Unit tests provided. (Add links if there are any)
• Integration tests provided. (Add links if there are any)

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines?
• Ran FindSecurityBugs plugin and verified report?
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets?

[brionmario]

This requirement is no longer valid since the feature is functioning as expected now.