🌱 Enhance Subcommand API

[Adirio]

Description

Subcommand.UpdateContext method was being used for both inserting cli related metadata to the subcommands and returning subcommand related metadata to the command constructor (cli). The Context struct didn't have anything to do with Go's context pacvkage which could also lead to harder to read code.

This PR uses the term Metadata instead of Context (which also has the advantage of not conflicting with onsi/ginkgo) and makes clearer differentioation between the input and output metadatas (cli->subcommand and subcommand->cli).

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[Adirio]

#1980 implements this with additional cleanups, please consider merging the other PR first (which will close this one) unless any of the other changes there are blocking and we want to merge this first.

[k8s-ci-robot]

@Adirio: PR needs rebase.

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