Add live migrate max downtime selector meta field

Adds a new flag to VM metadata to allow setting the VM live migration
max downtime. This will enable very busy VMs that hang live migration to
have this value changed.

api-daemon/migrations/versions/977e7b4d3497_pvc_version_0_9_89.py

@@ -0,0 +1,28 @@
+"""PVC version 0.9.89
+
+Revision ID: 977e7b4d3497
+Revises: 88fa0d88a9f8
+Create Date: 2024-01-10 16:09:44.659027
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = '977e7b4d3497'
+down_revision = '88fa0d88a9f8'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column('system_template', sa.Column('migration_max_downtime', sa.Integer(), default="300", server_default="300", nullable=True))
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column('system_template', 'migration_max_downtime')
+    # ### end Alembic commands ###