* [BREAKING] refactor: Decouple Checkpointing and Execution APIs
With this change, Checkpointing becomes an property of an IWorkflowExecutionEnvironment. This lets environments that are tightly-coupled to their CheckpointManager avoid needing to present APIs that would not work (e.g. taking in an InMemory CheckpointManager for Durable Tasks, for example)
* refactor: Normalize IsCheckpointingEnabled naming