Add timestamps to workflow and capability requests

• Add columns to tables workflow_requests and capability_requests
• Make the updated_at column auto-update in the database for both
• Use in the repr method for Python for human-friendliness

Manually verified that the timezone manipulations were correct

schema/versions/72cee10f1f0d_add_created_updated_timestamps_to_.py

+"""add created/updated timestamps to capability and workflow requests
+
+Revision ID: 72cee10f1f0d
+Revises: 50ff97fe0c2a
+Create Date: 2021-03-10 10:30:01.160958
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = "72cee10f1f0d"
+down_revision = "50ff97fe0c2a"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column(
+        "capability_requests",
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.func.now(),
+            nullable=False,
+        ),
+    )
+    op.add_column(
+        "workflow_requests",
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.func.now(),
+            nullable=False,
+        ),
+    )
+    op.add_column(
+        "capability_requests",
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.func.now(),
+            nullable=False,
+        ),
+    )
+    op.add_column(
+        "workflow_requests",
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.func.now(),
+            nullable=False,
+        ),
+    )
+
+    op.execute(
+        """
+    create or replace function update_updated_at_timestamp() RETURNS trigger LANGUAGE plpgsql AS $$
+    BEGIN
+      NEW.updated_at := current_timestamp;
+      RETURN NEW;
+    END;
+    $$;"""
+    )
+
+    op.execute(
+        """
+    create trigger capability_request_updated 
+    before update on capability_requests
+    for each row execute function update_updated_at_timestamp();"""
+    )
+
+    op.execute(
+        """
+    create trigger workflow_request_updated 
+    before update on workflow_requests
+    for each row execute function update_updated_at_timestamp();"""
+    )
+
+
+def downgrade():
+    op.drop_column("capability_requests", "created_at")
+    op.drop_column("workflow_requests", "created_at")
+    op.drop_column("capability_requests", "updated_at")
+    op.drop_column("workflow_requests", "updated_at")
+    op.execute("drop trigger workflow_request_updated on workflow_requests")
+    op.execute("drop trigger capability_request_updated on capability_requests")
+    op.execute("drop function update_updated_at_timestamp")