Add support in multiple places for OCI registries

[autodidaddict]

Proposed change

Nex should be able to start workloads based on layers described by an OCI manifest. Additionally, we should make it easy for developers to bundle up the various OS- and CPU- specific versions of a given tag (where applicable).

As such, the following is a list of proposed enhancements:

• When a workload start request has an artifact URL that uses the oci:// scheme, the appropriate CPU- and OS-specific binary (layer) should be downloaded from the registry
  • Figure out the best place to put registry credentials for accessing secure registries. This probably makes sense in the node configuration ?
• nex art should be a subcommand that helps people push binaries into an artifact in a registry
  • add a binary to an artifact
  • remove a binary from an artifact
  • push/pull binaries

Use case

Nex should be able to accommodate users that still want or need to integrate with OCI registries (this does not cover running OCI/docker workloads... only the artifact management)

Contribution

No response

[autodidaddict]

Note that this does not supercede #395 - this applies to oci:// workload URLs. Having the OS and CPU suffixes on plain keys in a NATS object store will still apply to nats:// artifact URLs.