Add support for silo identifier for multi-tenant login

[gschneider-r7]

Description

Adds an optional attribute for silo ID to NexposeSession.

Motivation and Context

Resolves #46 for multi-tenant login support.

How Has This Been Tested?

Not tested yet.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• [ ] I have updated the documentation accordingly (if changes are required).
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.