AWS GovCloud regions not supported

[jamessevener]

Describe the bug
AWS GovCloud regions to not match expected region

To Reproduce
Steps to reproduce the behavior:

1. Deploy k8s-pvc-tagger to AWS GovCloud hosted k8s cluster

Expected behavior
GovCloud regions are supported, and pods don't crash

Additional context
"level":"debug","msg":"ec2Metadata region","region":"us-gov-west-1"
"level":"fatal","msg":"Given AWS_REGION does not match AWS Region format."

k8s-pvc-tagger/aws.go

Line 43 in 66cc9e1

regexpAWSRegion = `^[\w]{2}[-][\w]{4,9}[-][\d]$`

Regex doesn't match for gov regions

[headkm]

A workable regex for this would be something like
^[\w]{2}[-][\w]{4,9}[-][\d]$|^[\w]{2}[-][\w]{3}[-][\w]{4,9}[-][\d]$