Add support of assume role with MFA

[the-demoss]

In our organization access to AWS CLI is implemented with assuming role and MFA and when I try to run ec2-instance-selector --profile <profile_name> --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/[email protected]/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.