Add DCO to docker plugin repo

[thepetk]

Which area is this issue related to?

/area ci

Issue Description

After the implementation of #878 the only repo in devfile org without DCO enabled is https://github.com/devfile/devfile-docker-plugin.

Acceptance Criteria

• Add DCO to https://github.com/devfile/devfile-docker-plugin

[github-actions]

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