Codepipeline cdk v2: Self mutate before synth step

### Describe the feature

Right now, i believe self mutate runs (if we set self Mutation to true in new CodePipeline(...) initialization) after synth step. What if i change commands in synth . And i need pipeline to update before it runs( so it can run the latest synth commands).

### Use Case

What if i change commands in synth . And i need pipeline to update before it runs( so it can run the latest synth commands).

### Proposed Solution

selfMutateFirst? : boolean

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

2

### Environment details (OS name and version, etc.)

Deployed to linux

Start at the CodePipeline(...) initialization and trace how the synth and self-mutation stages are ordered in CDK v2. Compare the current behavior with the proposed selfMutateFirst option, then define and verify the expected ordering and its effect when synth commands change.

Written by the indexing model from the issue text.