Replace -AT- with @ in change API provider list

[nimsara66]

Purpose

The current implementation introduced in [1] to address issue [2] does not replace -AT- with @ when listing APIs on the Change API Provider admin page for tenants. As a result, the process of changing the API provider has become unintuitive and inconsistent. This pull request aims to enhance the fix provided in [1] by addressing this gap. It is worth noting that the previous logic for listing APIs on the Change API Provider admin page followed a similar approach [3].

[1] #12679
[2] wso2/api-manager#3241
[3]

carbon-apimgt/components/apimgt/org.wso2.carbon.apimgt.persistence/src/main/java/org/wso2/carbon/apimgt/persistence/RegistryPersistenceImpl.java

Lines 1640 to 1641 in bf7e34d

	content.setProvider(
	RegistryPersistenceUtil.replaceEmailDomainBack(pubAPI.getProviderName()));

[tharindu1st]

@nimsara66 please fix any test case and add asserstion as well before merging