[transfer-Config] change users' realm when migrating to JFrog SaaS

[yannc21]

Is your feature request related to a problem? Please describe.
When migrating to JFrog SaaS, I'd like the possibility to switch to a new authentication mechanism, for example from LDAP (Self Hosted instance) to SAML SSO (SaaS instance).
For the moment, the Artifactory/Access API don't allow to change a user's realm.

Describe the solution you'd like to see
As the command triggers an Artifactory system export which includes the access export file, the code could modify that file as it contains all the users description

    "username" : "mary",
    "firstName" : null,
    "lastName" : null,
    "email" : "[email protected]",
    "realm" : "ldap",
    "status" : "enabled",

new params could be added such as --src-realm=ldap and --target-realm=saml which will replace any occurence of ldap by saml

Describe alternatives you've considered
the JFrog official recommendation is to ask each "ldap" user to log on the JFrog Platform via SAML which will either recreate their user in the target realm (like SAML) if the username is different from the initial one (ldap) or override the realm of the user if the login is the same for ldap and saml.

Additional context
NA