Add generator_operating_date to 860M changelog table (#3751)

* Add generator_operating_date to 860M changelog table

* Update release notes

docs/release_notes.rst

@@ -64,6 +64,11 @@ Data Cleaning
 * When ``generator_operating_date`` values are too inconsistent to be harvested
   successfully, we now take the last reported date in EIA 860 and 860M. See :issue:`423`
   and PR :pr:`3967`.
+* Added the ``generator_operating_date`` field into
+  :ref:`core_eia860m__changelog_generators`, adding 860M reported generator operating
+  dates into the changelog table. This table is not harvested, and thus does not affect
+  the ``generator_operating_date`` values reported in other core EIA tables. See
+  :issue:`3722` and PR :pr:`3751.`
 
 Bug Fixes
 ^^^^^^^^^

migrations/versions/52aa9f44b6a7_add_generator_operating_date_to_860_.py

@@ -0,0 +1,32 @@
+"""Add generator_operating_date to 860 changelog table
+
+Revision ID: 52aa9f44b6a7
+Revises: 49d2f4f7d7b7
+Create Date: 2024-07-29 18:15:06.462350
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = '52aa9f44b6a7'
+down_revision = '49d2f4f7d7b7'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('core_eia860m__changelog_generators', schema=None) as batch_op:
+        batch_op.add_column(sa.Column('generator_operating_date', sa.Date(), nullable=True, comment='Date the generator began commercial operation. If harvested values are inconsistent, we default to using the most recently reported date.'))
+
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('core_eia860m__changelog_generators', schema=None) as batch_op:
+        batch_op.drop_column('generator_operating_date')
+
+    # ### end Alembic commands ###

src/pudl/metadata/resources/eia860m.py

@@ -32,6 +32,7 @@
                 "energy_source_code_1",
                 "energy_storage_capacity_mwh",
                 "fuel_type_code_pudl",
+                "generator_operating_date",
                 "generator_retirement_date",
                 "latitude",
                 "longitude",