Update module path to sigs.k8s.io/cluster-api-provider-packet

[displague]

In this PR:

• package name was updated to sigs.k8s.io/cluster-api-provider-packet
• go mod tidy was run
• README badges were added (some referring to the new package name which won't work until after this is merged)
• golanglint-ci linter warnings were corrected (unused packageName, ineffectual assignment)
• Link was added to https://doc.crds.dev/github.com/kubernetes-sigs/cluster-api-provider-packet/ when discussing the PacketMachine spec

There are still references to packethost/cluster-api-provider-packet in the context of the Docker repo.

There are still references to kubernetes-sigs/cluster-api-provider-packet in the context of Github issues, releases, and workflows.

Closes #164

[deitch]

/lgtm

[deitch]

/approve

[k8s-ci-robot]

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