feat: Support packages defining pogo plugins to provide additional schema management.

[EdgyEdgemond]

my_package/pogo.py

from pathlib import Path

from pogo_core.util.plugins import Plugin


plugin = Plugin(
    migrations=Path(__file__).parent / "migrations",
    schema="my_package",
)

pyproject.toml

[project.entry-points.pogo]
my-package = "my_package.pogo"

closes #6

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.72%. Comparing base (2272b27) to head (dd446c9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #7      +/-   ##
==========================================
+ Coverage   97.60%   97.72%   +0.12%     
==========================================
  Files           8        9       +1     
  Lines         417      440      +23     
  Branches       52       56       +4     
==========================================
+ Hits          407      430      +23     
  Misses          6        6              
  Partials        4        4              

Flag	Coverage Δ
unittests	97.72% <100.00%> (+0.12%)	⬆️

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