DRY up the EDM connectors

[alexrichey]

I'm needed to add a connector for plan for our Dagster work, but the existing EDM Connectors are in a less than ideal shape. This refactors them, and adds a plan connector, which we'll invoke when plan recipes in Dagster.

We've got very, very comprehensive tests around this, so I feel confident about functionality. But I'm going to run a nightly_qa off it just to be a little more confident.

[codecov]

Codecov Report

❌ Patch coverage is 89.44724% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.76%. Comparing base (a142742) to head (38f2819).
⚠️ Report is 21 commits behind head on main.

Files with missing lines	Patch %	Lines
dcpy/connectors/edm/connectors.py	89.89%	13 Missing and 6 partials ⚠️
dcpy/models/connectors/edm/publishing.py	77.77%	2 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
dcpy/lifecycle/connector_registry.py	100.00% <100.00%> (ø)
dcpy/models/connectors/edm/publishing.py	93.33% <77.77%> (-3.89%)	⬇️
dcpy/connectors/edm/connectors.py	89.89% <89.89%> (ø)

... and 2 files with indirect coverage changes

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