.Net: Processes: Checkpoint state improvements

[esttenorio]

Description

• Checkpoint improvements that allow interacting with storage in particular times -> end of superstep, initialization only.
• Checkpoint allows "staging" states from process and steps and only uploading to cloud at the end of superstep
• Separating functionality available for process vs step
• Adding/Updating tests
• Adding simple cosmos db connector for LocalRuntime demo

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 😄