fix: Add Architecture Flexibility to Dockerfile

[celanthe]

This PR makes the following changes:

• Updates the Dockerfile to support both Intel-based (AMD64) and Apple Silicon-based (ARM64) Orka clusters by making the architecture configurable via build arguments.

Changes made:

• Added TARGETARCH build argument to the Dockerfile (defaults to amd64 for backward compatibility)
• Updated Orka CLI download URL to use the TARGETARCH variable instead of hardcoded amd64
• Added supporting documentation in the README explaining architecture support and build options

Internal JIRA ticket available upon request.

[relwell]

I'm curious what problem this solves. Especially since the Apple Silicon switch, I think most people are aware of how to address architecture inconsistencies with Docker. In general, the global solution is just to set DOCKER_DEFAULT_PLATFORM, and a quick googling will pull up even more succinct guidance on StackOverflow.

I'm a little hesitant to treat this as a specific enough problem to document or build explicit code around.

I do see that there is a problem around the architecture binary for the CLI. Can we not detect the architecture using something like uname and then dynamically download the appropriate binary?

[spikeburton]

Why are we talking about Apple silicon support here?

The runner binary is Linux based. It does not run on Apple silicon nodes right now.

I have the same question as @relwell - what is it we want to accomplish here?