WS-677: `null_dag` capability

Additions

• Added new capability: null_dag that simply launches the null_dag workflow
• Added button to launch new capability to the sandbox
• Changed "no-files" message to "No files are attached to this request."; added "no-parameters" message: "This request has no parameters."

Screenshot

New button

New empty-parameters/files messages

Completes WS-677 (for real this time)

schema/versions/c717f781828d_add_null_dag_capability.py

+"""add null_dag capability
+
+Revision ID: c717f781828d
+Revises: 990c5cd70082
+Create Date: 2021-09-15 14:58:45.780793
+
+"""
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "c717f781828d"
+down_revision = "990c5cd70082"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.execute(
+        "INSERT INTO capabilities (capability_name, capability_steps, max_jobs) VALUES "
+        "('null_dag', 'prepare-and-run-workflow null_dag\nawait-workflow', 2)"
+    )
+
+
+def downgrade():
+    op.execute("DELETE FROM capabilities WHERE capability_name = 'null_dag'")