feat: add client support for handling disabled accounts

[t-aleksander]

📖 Description

• makes the client use a new "enrolled" field to check whether the user has been already enrolled.
• prevents moving through enrollment steps if proxy returns an error

🛠️ Dev Branch Merge Checklist:

Documentation

• If testing requires changes in the environment or deployment, please update the documentation (https://defguard.gitbook.io) first and attach the link to the documentation section in this pool request
• I have commented on my code, particularly in hard-to-understand areas

Testing

• I have performed manual tests manually and all changes work
• New and existing unit tests pass locally with my changes

🏚️ Main Branch Merge Checklist:

Testing

• I have merged my changes before to dev and the dev checklist is done
• I have tested all functionalities on the dev instance and they work

Documentation

• I have made corresponding changes to the user & admin documentation and added new features documentation with screenshots for users/admins