Create migration to add CANCELLING to StateType enum

src/prefect/orion/database/migrations/MIGRATION-NOTES.md

@@ -8,6 +8,10 @@ Each time a database migration is written, an entry is included here with:
 
 This gives us a history of changes and will create merge conflicts if two migrations are made at once, flagging situations where a branch needs to be updated before merging.
 
+# Add `CANCELLING` to StateType enum
+SQLite: None
+Postgres: `50ab89b8fb35`
+
 # Add infrastructure_pid to flow runs
 SQLite: `7201de756d85`
 Postgres: `5d526270ddb4`

src/prefect/orion/database/migrations/versions/sqlite/2022_12_06_161948_50ab89b8fb35_add_cancelling_to_state_type_enum.py

@@ -0,0 +1,22 @@
+"""Add CANCELLING to state type enum
+
+Revision ID: 50ab89b8fb35
+Revises: 7201de756d85
+Create Date: 2022-12-06 16:19:48.316823
+
+"""
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "50ab89b8fb35"
+down_revision = "7201de756d85"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.execute("ALTER TYPE state_type ADD VALUE IF NOT EXISTS 'PAUSED';")
+
+
+def downgrade():
+    pass