feat(datasets): Added the Experimental PolarsDatabaseDataset

[MinuraPunchihewa]

Description

This PR adds the PolarsDatabaseDataset to support interactions with databases using Polars.

Fixes #853

Development notes

I have extended the SQLQueryDataset to implement this dataset.

These changes have been tested,

1. Manually, by running the code locally to load and save tensors from and to Safetensors files.
2. Via the existing and newly added unit tests.

Checklist

• Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• Updated the documentation to reflect the code changes
• Added a description of this change in the relevant RELEASE.md file
• Added tests to cover my changes
• Received approvals from at least half of the TSC (required for adding a new, non-experimental dataset)

[MinuraPunchihewa]

Hey @noklam, @deepyaman,
I was able to come up with this implementation for the PolarsDatabaseDataset by extending SQLQueryDataset and it seems to work quite well (at least load() does).

Should we implement save() as well? This would require a table name to be provided as parameter.

Or do you have different thoughts on how this dataset ought to be implemented?