feat: Support MSSQL storage

[jamar-criteo]

Description

What changes are made to solve it?

References

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[aaguiarz]

@jamar-criteo the team does not have the bandwidth to review this RFC now. We don't have a time to share yet.

@DanCech and team are testing an extensibility mechanism for additional databases with gRPC. Once we have more clarity about that approach, we'll communicate it.

[jmezach]

We would like to adopt OpenFGA but are currently blocked from adopting it since we're running entirely on MS SQL Server so we would welcome a SQL storage implementation.

[praveenr1793]

We’re planning to implement OpenFGA, but since our environment runs exclusively on Microsoft SQL Server, we’re unable to move forward. Is there any timeline when the update is likely to be rolled out?

[praveenr1793]

Is there a ABC or protocol that we can use to implement for Azure SQL based storage?