Move execution of the unit tests of the mutation handlers to its own packages

[supershal]

Currently all handler patches are running as a single unit test for each provider.
Ex. AWS: https://github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/blob/main/pkg/handlers/aws/mutation/metapatch_handler_test.go
Docker: https://github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/blob/main/pkg/handlers/docker/mutation/metapatch_handler_test.go

In addition to running these tests for each provider, we should also run this test from the handler package. For example, the mirror handler related tests should be able to executed from mirror or mirror/test package. https://github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/tree/main/pkg/handlers/generic/mutation/mirrors/tests

This might create some duplication of execution of the tests but it will be convenient to execute package level tests during development.

[supershal]

d2iq-labs#21 and d2iq-labs#23 addresses this issue