Fix the issue in the self-registration flow when the email address is configured as a unique value

[DilshanSenarath]

Purpose

This PR resolves issues in the self-registration flow when the email address is configured as a unique value. Previously, if a user entered an already registered email, they were redirected to an error page without an option to enter a different email and continue the registration process. This PR addresses that by including the email field on the error page. Additionally, it fixes an issue where, even with a valid email, the password fields would trigger an 'empty password' error. These issues are now resolved with this PR.

Related Issue

• https://github.com/wso2/product-is/issues/21567
• https://github.com/wso2/product-is/issues/21579
• https://github.com/wso2/product-is/issues/21565

[wso2-jenkins-bot]

🦋 Changeset detected

The changes in this PR will be included in the next version bump.

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