feat: Add metadata as input for compute_instance

[JudexGrim]

Exposed metadata attribute of compute_instance_from_template as an input for the compute_instance module.

This allows for setting custom metadata and overriding template metadata, allowing for custom startup scripts and other keys for each compute instance made from one template.

Note: I closed the pull request I made from my alternative account and opened it from this one. my apologies.

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