Adjust IndexKind and DistanceFunction defaults

[milderhc]

Motivation and Context

Description

• Make vector attribute to receive an IndexKind enum.
• Add UNDEFINED to IndexKind and DistanceFunction to have them as default in the vector attribute. When values are undefined each database defines its default.
• Update file creation in SQLite tests.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄