[Improvement] In the Gravitino CLI/Java API you can delete the anoymous user

[justinmclean]

What would you like to be improved?

The Gravitino CLI allows you to delete the anonymous user. It does ask if are you sure, but this can have bad side effects.

If you try to create a role after this you get the error:

Failed to operate role  [admin] operation [CREATE] under metalake [metalake_demo], reason [Current user anonymous doesn't exist in the metalake metalake_demo, you should add the user to the metalake first]

You can recreate a user called anonymous to fix this error, but I'm not sure if that has other side effects. I'm assuming this may be an issue with the REST interface and Java API and not just the CLI.

How should we improve?

Change the Java API so this is not possible?