AWS profile support

[hypnoglow]

Ref: #5 (comment) #5

This cannot be fully implemented via --profile flag, because you cannot pass it to native helm commands, in case of s3 protocol usage (example: helm repo add myrepo s3://mybucket/charts).

AWS CLI also supports named profiles via AWS_PROFILE environment variable. So, adding AWS_PROFILE support for helm-s3 will be trivial and will work for all cases.