az ml job create should respect .gitignore files in parent directories

**Related command**
az ml job create

**Is your feature request related to a problem? Please describe.**
When running `az ml job create` for a pipeline, folders like `__pycache__` are uploaded into the snapshot from every component in the pipeline.

These are excluded in a parent directory .gitignore (the same directory the pipeline yaml is defined in), and yet the CLI does not respect these.

There was an issue previously reported here - https://github.com/Azure/azureml-previews/issues/111 - and .amlignore/.gitignore support is mentioned in the docs: https://docs.microsoft.com/en-us/azure/machine-learning/how-to-create-machine-learning-pipelines#submit-the-pipeline - but it would appear you have to place a .gitignore in the folder of every component?

**Describe the solution you'd like**
For the CLI to respect the .gitignore hierarchy.