[Request] Provide Key Vault Secret Store Service in the IoT Operations SDK

[uriel-kluk]

The IoT Operations SDK currently provides a StateStore service, which is extremely useful for building connectors that rely on distributed state. However, the SDK does not offer an equivalent secret store abstraction backed by Azure Key Vault.
Many connectors need to access securely:

• connection strings
• device credentials
• shared access keys
• certificates
• tokens
• enrollment secrets

Right now, each connector must interact directly with Azure Key Vault. This requires developers to handle:

• credential setup
• Managed Identity configuration
• retries and throttling behavior
• API versioning
• dependency injection
• secret refresh logic

This creates duplication and inconsistency across SDK‑based components.