Support pagination for getting users

[KamikazeZirou]

Description

Now, GetUsers return all users and doesn't support pagination. GetUsers uses Slack API users.list and users.list supports paging. So, this SDK can get users with paging.

The number of users can be over 1,000 and more. This isn't few.
I think it is better to support pagination for getting users.

(Optional) Slack's documentation

https://api.slack.com/methods/users.list

Note

I'm replacing code using raw slack API with code using this SDK.
Then, I found GetUsers doesn't support pagination.

My implementation is #1465.

[KamikazeZirou]

@nlopes

Could you see this issue?

[nlopes]

Yep, have planned a session to go over all of the current open issues tomorrow!

[KamikazeZirou]

Yep, have planned a session to go over all of the current open issues tomorrow!

Thanks!