Root user should not be reassigned other roles in space

[nianiaJR]

Describe the bug (must be provided)
At now root user can be assigned to other roles in a space, it's confused for user which the real access he owns in the space?

Accoding to my test, if I'm the root user of one nebula db which includes a space test

$ GRANT ROLE User ON test TO root

SHOW ROLES IN test; It's seems that I'm the user role of the space test, but I can modified the schema becaused of the db root role.

User Role in space

Create TAG is allowed

Additional context
According to the confusing behavior of the role managing, it may cause some problems in applications about nebula.🤝

[HarrisChu]

why grant role to root? this scenario is not meaningful.

just like in linux system, root is the super admin for nebula cluster.

[Shylock-Hg]

Yes, I think we should disable it.

[CPWstatic]

Emmm, we also have a role named GOD. The total access control and role are not well designed.

[Sophie-Xie]

@slimshadylol0303 Please take a look at this question, you can combine it with role optimization.