Add support of assume role with MFA

In our organization access to AWS CLI is implemented with assuming role and MFA and when I try to run `ec2-instance-selector --profile --vcpus 4 --memory 8 --region eu-central-1` for example it fails with:

```
panic: AssumeRoleTokenProviderNotSetError: assume role with MFA enabled, but AssumeRoleTokenProvider session option not set.

goroutine 1 [running]:
github.com/aws/aws-sdk-go/aws/session.Must(...)
/go/pkg/mod/github.com/aws/aws-sdk-go@v1.38.27/aws/session/session.go:370
main.getRegionAndProfileAWSSession(0xc0003362b, 0xc00033627, 0xc00033627, 0xc00033627, 0xc00033061)
/amazon-ec2-instance-selector/cmd/main.go:315 +0x790
main.main()
/amazon-ec2-instance-selector/cmd/main.go:182 +0x148
```

It will be great to have this functionality.