Backport of Dockerfile: Remove gnupg from Consul k8s container into release/1.0.x

[thisisnotashwin]

Backport

This PR is auto-generated from #1882 to be assessed for backporting due to the inclusion of the label backport/1.0.x.

WARNING automatic cherry-pick of commits failed. Commits will require human attention.

merge conflict error: POST https://api.github.com/repos/hashicorp/consul-k8s/merges: 409 Merge conflict []

The below text is copied from the body of the original PR.

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Changes proposed in this PR:

• gnupg is likely an artifact from pre-CRT days when we used to validate Consul K8s releases ourselves for publishing with Docker. This is is likely not needed so will attempt removing it.

How I've tested this PR:

• Acceptance tests

How I expect reviewers to test this PR:

Checklist:

• Tests added
• CHANGELOG entry added

  HashiCorp engineers only, community PRs should not add a changelog entry.
  Entries should use present tense (e.g. Add support for...)

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Overview of commits

• 4f4358e - e610149 - 3d97178