Add integration tests

[dkoshkin]

Add integration tests with envtest (or similar) to test meta handler patches.

The goal is to pass is some input that resembles user provided input, possibly a Cluster object with different variables set, and get output of different CAPI objects with the patches applied to them.

Some possible use-cases to test:

• Creating a global image registry mirror
• Air-gapped AWS cluster with unmanaged infra
• FIPS configuration

In order to support this, envtest must run this webhook, the regular CAPI webhook, and any related topology reconcilers.