actions: Add --oci flag to call OCI launcher

[dtrudg]

Description of the Pull Request (PR):

Depends on #1021

Add an --oci flag to actions (run/shell/exec) that calls the (no-op) OCI launcher instead of the singularity native runtime launcher.

Fix OCI launcher supported option checks for empty structs (not just nils), and always set options.

Add E2E profiles and a test for unimplemented error on the --oci option.

This fixes or addresses the following GitHub issues:

• Fixes #1022

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