feat: implement standard completion command

[alexanderankin]

so that you can do "oci completion bash" like you would with kubectl, gh, docker, etc

this pr also introduces a refactor to get the paths of the files to print for bash and powershell so that powershell can be supported in the future. tools frequently support other shells like fish zsh etc

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[alexanderankin]

THIS PR IS LICENSED WITH https://opensource.org/license/mit-0 - I give permission to merge this code without attribution to myself. just rewrite the commit as yourself or whatever