[Feature][Improvement] Introduce tenant-wise username input validation.

[Thumimku]

Epic: https://github.com/wso2-enterprise/iam-engineering/issues/648
Currently IS has username validation can be set on user store level.
Email as user name can be configured also https://is.docs.wso2.com/en/latest/guides/identity-lifecycles/enable-email-as-username/

But what we need a tenant-wise username validator where the admin can enforce rule based validators such as min, max character efficiently.

[Thumimku]

Postponing to alpha cause we need tenant qualified URL feature to be enabled

[Thumimku]

Integration test for REST API: #16983

[Thumimku]

We are not delievering this feature as per the mail due to a functional limitaiton,
check: [Unification] Bring new tenant level Password/username validation feature to IS

[Thumimku]

@bhagyasakalanka is working on removing the feature from input validation listener.
@bhagyasakalanka can you please update the status?

[bhagyasakalanka]

Integration tests are fixed with: #17508
Username Input validation disable for IS: wso2/carbon-identity-framework#5106

[bhagyasakalanka]

wso2/identity-apps#4442