Backport: Allow skipping the redundant Pulp CLI publish after RPM uploads

What does this MR do and why?

Backport of 55760b4a (!9951 (merged)) to 19-3-stable.

Allow uploading RPM packages to Pulp with pulp rpm content upload --no-publish, when the CI/CD variable PULP_CLI_PUBLISH is false. The Pulp RPM repositories have autopublish enabled, so Pulp already publishes the repository inside the upload task. The second publish from the pulp CLI was redundant, and it caused most of the repository lock contention that made the staging upload jobs time out.

By default (PULP_CLI_PUBLISH unset or true), the CLI publishes after each upload as before. This backport lets the release pipelines of this stable branch use the variable too.

Related to gitlab-com/gl-infra/delivery#22495 (closed)

MR acceptance checklist

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• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The original MR has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).

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