Address test warnings

[kevin-bates]

This pull request is a "first pass" at addressing the warnings produced following the server CI tests. Prior to this PR 3791 warnings were produced. This PR takes the warnings down to 474 (87%) and when merged with #2829, the warnings will be around 55 (98%). (Note, these values were produced on my local dev env. In running CI on my fork, and without #2829, I still see 2108 warnings, but 474 on my local system. I suspect the additional warnings are related to recent deprecations in tornado regarding event loop management and I'm running with an older version.)

The primary issue here was in handling class initialization parameters within the Configurable class hierarchy. The PR currently has two commits, each taking a different approach to resolving the issue.

• The first was to add a positional argument (for the most part root_dir) so that it is not included in the **kwargs that flow to the superclasses. This approach probably consisted of fewer changes than the second because that was closer to what was happening before.
• The second approach was to use **kwargs but pop parameters like root_dir out, so that it doesn't interfere in the superclasses. This approach was chosen because I found it was used within the traitlets package, lending credence to that approach.

I also refactored the PipelineProcessorResponse class, introducing a RuntimePipelineProcessorResponse class. The KFP and Airflow response objects derive from the latter while the Local response object derives directly from PipelineProcessorResponse since it doesn't need the location information in the response and was just passing empty string placeholders for those values. In addition, this class hierarchy now mirrors that of the PipelineProcessor class hierarchy.

In some cases, you'll see the __init__() method completely removed. This is intentional as it is not required if the traitlet (e.g., root_dir) is the only item needed from the **kwargs and is functionality the traitlets package provides automatically.

I'm going ahead and marking #2782 as resolved by this PR since most all of the remaining errors can be attributed to upstream components (Tornado, KFP, and Papermill) and should probably be addressed with separate issues for each.

Resolves: #2782

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[ptitzler]

LGTM! Without those warnings, it's now much easier to identify test issues. Much appreciated!

[kiersten-stokes]

In some cases, you'll see the init() method completely removed. This is intentional as it is not required if the traitlet (e.g., root_dir) is the only item needed from the **kwargs and is functionality the traitlets package provides automatically.

Cool! LGTM