Add client config option + registry auth e2e tests

[darkowlzz]

• Adds a --registry-config-dir flag in VM create, image import and kernel import subcommands.
• Adds field registryConfigDir in ignite configuration.
• Update v1alpha4 API and add custom conversion function for v1alpha3.
• Adds setup-private-registry.sh script to setup a local docker registry with self-signed cert and basic auth.
• Adds test util to delete image from ignite and the runtime content store.
• Adds e2e tests for image import with configurations set via flag and ignite configuration.
• Update go version in semaphore to 1.16.3 to use os.WriteFile().

Follow-up of #833

TODO:

• [x] Update ignite configuration docs to add examples of registry configuration option.
• [x] Add an option to toggle insecure skip verify in TLS client of containerd remote registry resolver.
• [x] Maybe an option to support plain http in remote registry resolver.

[stealthybox]

It's good to see the test runtime for this is actually quite good on Semaphore.

36s - Registry Setup 26s - TestPullFromAuthRegistry

1m02s

[stealthybox]

🎉