Fixed Auth Mechanism for ScyllaDB/Cassandra

[MinuraPunchihewa]

Description

This PR fixes the auth mechanism for the ScyllaDB handler (and as a result, the Cassandra handler) to enforce it only if the parameters are provided.

Fixes #9215

Type of change

• 🐛 Bug fix (non-breaking change which fixes an issue)

Verification Process

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• Test Location: Specify the URL or path for testing.
• Verification Steps: Outline the steps or queries needed to validate the change. Include any data, configurations, or actions required to reproduce or see the new functionality.

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Checklist:

• My code follows the style guidelines(PEP 8) of MindsDB.
• I have appropriately commented on my code, especially in complex areas.
• Necessary documentation updates are either made or tracked in issues.
• Relevant unit and integration tests are updated or added.