Identifier first step is always validating whether the user exists locally

[ThaminduDilshan]

Describe the issue:
$subject

How to reproduce:
Add identifier first step and other authenticators for the 2nd step.
During the login unable to proceed without a valid user locally in the system

Expected behavior:
Identifier first should not always validate whether there is a user locally in the system. In cases where IdP discovery happens over identifier first, those will break.

[ThaminduDilshan]

This fix will move the server level "ValidateUsername" authenticator config into the adaptive script parameter, where the server config will get overridden by the adaptive property. The user resolution behavior would be as follows.

if skipIdentifierPreProcess == "true":
    skipAll;

else:
    if emailUserNameValidationEnabled == true:
        validateUsername();

    if multiAttributeLoginEnabled == true:
        resolveUser();

    if ValidateUsername(adaptive) == true:

        if B2B tenant:
            resolveB2BUser();

        else:
            resolveUser();

    if ValidateUsername(adaptive) == false:
        // Skip user resolution

    if ValidateUsername(adaptive) == null && ValidateUsername(server) == true:
        resolveUser();