Update User model comments about permissions

[wxiaoguang]

Copied from and close #17467

Please help to check whether my understanding and comments are correct.

[Gusted]

The descriptions are good(if I've read the code correctly) and describes what the fields are, I think the wording need a little bit of change and maybe clarify some things up.

[Gusted]

Suggested change

	// true: user is not allowed to log in Web UI. Git SSH access could still be allowed.
	// true: user is not allowed to log into the Web UI. Git SSH access could still be allowed.

I think Git SSH access >could< still be allowed. that could could be clarified, as in, which conditions the Git SSH access is allowed.

[wxiaoguang]

The conditions belong to SSH access module, User model has nothing to do (no knowledge) about it.

If we need to clarify the conditions, related comments should be written in SSH access module.

[Gusted]

I dont have a problem if its clarified to the SSH access module.

For someone who's trying understand what a field does and it refers to something that isnt described somewhere, then I would personally still not fully understand what the field does.

[wxiaoguang]

Got it. I just added a new comment: "please refer to Git/SSH access related code/documents".

[Gusted]

The prohibtedLogin could be done in another PR as this is just for the user struct. LGTM