Support ifNotExists in add column

[KodaiD]

Description

This PR adds the support for ifNotExists option in add column operation of ScalarDB. With this option, users can avoid errors when trying to add a column that already exists in the table.

Related issues and/or PRs

N/A

Changes made

• Added ifNotExists parameter to the addNewColumnToTable method in Admin interface.
• Added integration tests to verify the behavior of ifNotExists option.

Checklist

• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes.
• I have considered whether similar issues could occur in other products, components, or modules if this PR is for bug fixes.
• 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

Added support for ifNotExists option in add column operation.

[komamitsu]

LGTM! 👍

[brfrn169]

LGTM! Thank you!

[feeblefakie]

LGTM! Thank you!

[Torch3333]

LGTM, thank you!