Atomic save (rollback implementation)

The current implementation of the `SavePipeline` command assumes implements the happy path only.
This may lead to inconsistent states where in `Nested Pipelines` the child pipelines are updated without the parent being updated due to an error.

Plan and implement an Atomic save construct that rolls back the `Nested Pipelines` save operation in case of an error.

Start by reading the SavePipeline command and tracing how Nested Pipelines are saved. Identify the state changes made for child and parent pipelines, then define the rollback boundary for errors. Done means a failed nested save leaves the parent and child pipelines in their original state.

Written by the indexing model from the issue text.