Show only the email field in the regsitration field when the email as username is enabled

[sahandilshan]

Purpose

$subject The UI will look as below when the email as the username is enabled and the following configuration is set to true in the deployment.toml

[accountrecoveryendpoint]
hide_username_when_email_as_username_enabled = true

Enabled

Disable

Related Issue(s)

• https://github.com/wso2/product-is/issues/21411

[CLAassistant]

All committers have signed the CLA.

[wso2-jenkins-bot]

🦋 Changeset detected

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

Not sure what this means? Click here to learn what changesets are.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Please upload report for BASE (master@8620104). Learn more about missing BASE report.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #7097 +/- ## ========================================= Coverage ? 31.79% ========================================= Files ? 41 Lines ? 890 Branches ? 204 ========================================= Hits ? 283 Misses ? 607 Partials ? 0 ``` | [Flag](https://app.codecov.io/gh/wso2/identity-apps/pull/7097/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | Coverage Δ | | |---|---|---| | [@wso2is/core](https://app.codecov.io/gh/wso2/identity-apps/pull/7097/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | `31.79% <ø> (?)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2#carryforward-flags-in-the-pull-request-comment) to find out more.