Dynamically filter out invalid instance types

[mselim00]

Description of changes:
Leverage EC2:DescribeInstanceTypes API to dynamically scope down default instance types list to only those that exist in the test region.

Relies on error format:

operation error EC2: DescribeInstanceTypes, https response error StatusCode: 400, RequestID: <request_id>, api error InvalidInstanceType: The following supplied instance types do not exist: [<instance_type(s)>]

Specifically, the error handler relies on the presence of InvalidInstanceType in the error string, a printed list of the instance types being discoverable by indexing the last occurrence of a forward square bracket ([), and multiple types being separated by a comma and a space (, ).

Tested this by appending ec2types.InstanceTypeTrn1n32xlarge to the defaultInstanceTypes_x86_64 array and then creating a test deployment in us-west-1. Verified that the 'Eliminating instance type' log line was hit only for trn1n.32xlarge and that node groups create.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[cartermckinnon]

You should be able to check the error code here like:

if err != nil {
	var apierr smithy.APIError
	if errors.As(err, &apierr) {
		// do something with apierr.ErrorCode()
    }
}

instead of doing the parsing yourself

[mselim00]

Just pushed a change to parse the error code in this format and pass just the error message to the invalid instance types parser rather than the whole error.

[cartermckinnon]

Just some nits 👍