Update Dockerfile for release/v6.1.x

[chatton]

Description

ref: #3068

• This PR: updates Dockerfile for this release branch
• Adds basic test to ensure the image builds (note the ibc-go version specified here doesn't matter as we are just building the image)
• Pass a build arg when we release the image.

Commit Message / Changelog Entry

N/A

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• Targeted PR against correct branch (see CONTRIBUTING.md).
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards and Go style guide.
• Wrote unit and integration tests.
• Updated relevant documentation (docs/) or specification (x/<module>/spec/).
• Added relevant godoc comments.
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