Adds check for whether file exists locally
case 1: local (relative) file does not exist
```
foo:
name: "[job-output] test-job by shreyas"
tasks:
- task_key: my_notebook_task
existing_cluster_id: ***
notebook_task:
notebook_path: "./doesnotexist"
```
output:
```
shreyas.goenka@THW32HFW6T job-output % bricks bundle deploy
Error: notebook ./doesnotexist not found. Error: open /Users/shreyas.goenka/projects/job-output/doesnotexist: no such file or directory
```
case 2: remote (absolute) file does not exist
```
foo:
name: "[job-output] test-job by shreyas"
tasks:
- task_key: my_notebook_task
existing_cluster_id: ***
notebook_task:
notebook_path: "/Users/shreyas.goenka@databricks.com/doesnotexist"
```
output:
```
shreyas.goenka@THW32HFW6T job-output % bricks bundle deploy
shreyas.goenka@THW32HFW6T job-output % bricks bundle run foo
Error: failed to reach TERMINATED or SKIPPED, got INTERNAL_ERROR: Task my_notebook_task failed with message: Notebook not found: /Users/shreyas.goenka@databricks.com/doesnotexist. This caused all downstream tasks to get skipped.
```
case 3: remote exists
Successful deploy and run
Files with extension `.ipynb` are imported are Jupyter notebooks.
This code detects 1) if the file is a valid Jupyter notebook and 2) the
Databricks specific language it contains.
shreyas-goenka
Pieter Noordhuis