[3.10, 3.11, 3.12] Backport data loader

[brfrn169]

Description

This PR backports several PRs related to ScalarDB Data Loader to 3.10, 3.11, and 3.12.

Related issues and/or PRs

• Add empty dataloader CLI and core sub projects #1726
• Add picocli argument convertor for column key value and file format #1742
• Add export --output-file flag and validation #1754
• Add mockito and core project in Gradle files #1769
• Move ColumnKeyValue to the data loader core project #1770

Changes made

• Backported several PRs

Checklist

• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes.
• Any remaining open issues linked to this PR are documented and up-to-date (Jira, GitHub, etc.).
• Tests (unit, integration, etc.) have been added for the changes.
• My changes generate no new warnings.
• Any dependent changes in other PRs have been merged and published.

Additional notes (optional)

N/A

Release notes

N/A