CLOUDP-280230: Replace launcher with contract helper

[josvazg]

Simplify contract testing:

• No TestMain preparations required.
• No need for external YAML files for infrastructure.
• No need for a AKO helm version, latest will be used by default.
• No explicit skipping and cleaning, it happens within the contract test run wrapper.
• No hard dependency of the helper in kind, assumes a working k8s config is available, which CI and make provide easily.

Note: Using make locally, the contract tests launch kind with them. On the CI, this is not needed because the workflow launched kindalready before running the tests, so we use an existing env var in the launch script to avoid launching kind again.

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https://app.codecov.io/github/mongodb/mongodb-atlas-kubernetes/commit/c7b2de002b02e921911b90f672e7380a682bf91e

[josvazg]

CLOUDP-280230