feat(content-docs): Add overwrite option for docs:version command

[fflaten]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

Allow overwriting an existing versioned docs.

Example usage: Using current docs for preview builds of minor/patches and replacing the latest major-versioned docs on GA release.

Test Plan

Added tests for CLI validation and expected behavior based on existing tests. Tested locally with an existing docusaurus site (without localization).

Test links

Updated versioning docs section: https://deploy-preview-12278--docusaurus-2.netlify.app/docs/versioning/#updating-an-existing-version

Related issues/PRs

Fix #3478

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