DM-35803: Add DataFrame delegate to enable InMemoryDatasets of DataFrames.

[erykoff]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Merging #720 (b0940af) into main (bf1ffe9) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head b0940af differs from pull request most recent head 3a7b71e. Consider uploading reports for the commit 3a7b71e to get more accurate results

@@            Coverage Diff             @@
##             main     #720      +/-   ##
==========================================
- Coverage   84.63%   84.62%   -0.01%     
==========================================
  Files         243      243              
  Lines       32013    31990      -23     
  Branches     6004     6003       -1     
==========================================
- Hits        27093    27071      -22     
+ Misses       3748     3747       -1     
  Partials     1172     1172              

Impacted Files	Coverage Δ
...n/lsst/daf/butler/registry/interfaces/_datasets.py	73.68% <0.00%> (-2.21%)	⬇️
python/lsst/daf/butler/registry/_registry.py	72.67% <0.00%> (-0.30%)	⬇️
python/lsst/daf/butler/registries/sql.py	81.08% <0.00%> (-0.04%)	⬇️
python/lsst/daf/butler/registry/tests/_registry.py	99.22% <0.00%> (-0.01%)	⬇️
python/lsst/daf/butler/__init__.py	100.00% <0.00%> (ø)
python/lsst/daf/butler/registries/remote.py	0.00% <0.00%> (ø)
.../butler/registry/datasets/byDimensions/_storage.py	84.39% <0.00%> (+<0.01%)	⬆️

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[timj]

Thank you for adding this. Lots of minor comments to consider but no big issues.