test: pkg/aws

[skl]

Refactored dependency on *prometheus.Registry struct to provider.Registry interface to support mocking.

New still needs work but this PR introduces gomock as necessary to create compatible mocks in this package, mockery-generated mocks were not type-compatible for some reason.

Note that this means there are duplicate mocks generated for the new interface.

79% coverage.

[skl]

As suspected, this error has come back due to the hard dependency on AWS:

=== RUN   Test_New
=== RUN   Test_New/no_error
    aws_test.go:29: 
        	Error Trace:	/home/runner/work/cloudcost-exporter/cloudcost-exporter/pkg/aws/aws_test.go:29
        	Error:      	Received unexpected error:
        	            	operation error ec2imds: GetRegion, failed to get API token, operation error ec2imds: getToken, http response error StatusCode: 400, request to EC2 IMDS failed
        	Test:       	Test_New/no_error
--- FAIL: Test_New (0.00s)
    --- FAIL: Test_New/no_error (0.00s)

I'll skip the test for now (coverage dropped to 34.5%), that refactor is probably worth a separate PR.

[Pokom]

🚀 Checked out locally and ran everything, all the exporters are still working as expected. Curious to see what the refactor will look like to improve coverage!