api,account,console: Allow shorter user IDs

[htdvisser]

Summary

This pull request lowers the minimum length of user IDs to 2, for better compatibility with v2 ID restrictions.

Closes #3723.

Testing

Should be covered by existing tests

Regressions

This may not (immediately) work with external integrations that work with user IDs and use the same validation rules as we did.

Notes for Reviewers

n/a

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.