[Experimental] Use zstd compression in Docker builds

[jrmccluskey]

Swaps out the standard gzip compression in Docker container builds for zstd, reducing container sizes when compressed and improving decompression speeds. Allows for specifying other compression libraries as a flag.

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[jrmccluskey]

@gemini-code-assist review

[gemini-code-assist]

Code Review

This pull request introduces support for Docker image compression (defaulting to 'zstd') in the BeamDockerPlugin Gradle plugin, configuring the --output build arguments based on whether the image is being pushed or loaded. A critical issue was identified where the type=docker exporter (used when loading images locally) does not support compression parameters, which will cause local builds to fail. It is recommended to fall back to the standard --load option when ext.load is true.

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[jrmccluskey]

R: @damccorm

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