Allow multiple folders in class_package node registration key

[parul-l]

Description

In this PR we allow the class_package key in the metadata portion of the primrose config to be a list of folders to search for potential node candidates. For example, given the folder structure

├── config
│   ├── my_primrose_config.yml
├── src
│   ├── readers
│   │   ├── reader_node.py
│   ├── pipelines
│   │   ├── pipeline_node.py
├── sample_project
│   ├── sample_project_node.py

we can specify the potential node candidate folders in the metadata as:

metadata:
  class_package:
    - './src'
    - './sample_project'

implementation_config:
  reader_config:
  ...

This allows our DAG to use nodes from both the src and sample_project folders.

Types of change

Enhancement

Checklist

• I squashed my commits to a reasonable number of descriptive commits.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[briangrahamww]

Is this to patch something for an existing project or for new dev?

[parul-l]

Is this to patch something for an existing project or for new dev?

New development.

[briangrahamww]

Approving since we need to resolve this issue to move forward with internal projects. We will keep the changes in master and not do a release until the pygraphviz error is resolved.