enhance: Add Describe User methods

[punkerpunker]

resolves: #698

I've added an entity:

type UserDescription struct {
	Name  string
	Roles []string
}

And two methods and tests for them:

• DescribeUser(ctx context.Context, username string) (entity.UserDescription, error) - which returns UserDescription for a specific user.
• DescribeUsers(ctx context.Context) ([]entity.UserDescription, error) - which returns UserDescription for all users presented.

The thing that I want to raise is that I am not sure if it is feasible to return empty UserDescription entity in case the user from DescribeUser method doesn't exist, I would highly appreciate suggestions here.

Also, I am not much familiar with the milvus-sdk-go codebase and this is my first PR here, so any comments/feedback/suggestions would be highly appreciated, thanks!

[sre-ci-robot]

Welcome @punkerpunker! It looks like this is your first PR to milvus-io/milvus-sdk-go 🎉

[punkerpunker]

Failing tests doesn't seem to be related to this specific change btw

[congqixia]

@punkerpunker thanks for the contribution. I've fixed failing cases. could you please rebase and fix the lint issue reported in lint action?

[punkerpunker]

@congqixia seems like fixed

[congqixia]

/kind enhancement

[punkerpunker]

Thanks @congqixia, once again the tests falling doesn't seem to be related to the change :)

[punkerpunker]

Hey @congqixia, are we concerned about something in particular so we didn't merge this one yet? Want to start working on tf-provider, and that piece is missing :)

Let me know if I can help in any way

[congqixia]

@punkerpunker sorry for the late reply. Master branch e2e cases was unstable due to rapid change of milvus master behavior. We have just fixed the cases. You can rebase your PR now

[congqixia]

/lgtm

[sre-ci-robot]

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