CLI does not support custom AWS profile names

[TreehouseFalcon]

What type of feature request is this?

• [ ] Mantle doesn't support a Roblox feature I would like to use
• [x] Mantle CLI improvement
• [ ] Other

Describe your problem

The Mantle CLI currently does not allow us to change the AWS CLI profile name used for S3 authentication.

Describe the solution you'd like

The rusoto::ProfileProvider should be fed an optional profile name from MANTLE_AWS_PROFILE.