Should return true for system namespace in namespaceExists()

[brfrn169]

Description

This is for the 3 branch.

Currently, when the system namespace is not created yet, the getNamespaceNames() API returns the system namespace but the namespaceExists() API with the system namespace returns false. This PR addresses this issue.

Related issues and/or PRs

• Support listing namespaces for ScalarDB v3 #2002

Changes made

• Added check for the system namespace to namespaceExists() for each storage adaptor.

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

[komamitsu]

LGTM! 👍

[Torch3333]

LGTM, thank you!

[feeblefakie]

LGTM! Thank you!