Add support for get voice state

[Puncher1]

Summary

This PR adds the functionality to get the voice state over the http endpoints.

Related PR:

• Document get voice state endpoints discord/discord-api-docs#7061

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

[chredeur]

It would be nice to merge this functionality 😅

[Rapptz]

It's not clear from the documentation what would happen if the member does not have a voice state. I'm assuming it returns a 404, but I'm not at liberty to test.

[MCausc78]

It's not clear from the documentation what would happen if the member does not have a voice state. I'm assuming it returns a 404, but I'm not at liberty to test.

Yes, it returns 404 with "Unknown Voice State" message.

[Puncher1]

It's not clear from the documentation what would happen if the member does not have a voice state. I'm assuming it returns a 404, but I'm not at liberty to test.

Yes it does

[Rapptz]

Should probably add that to the Raises section then.