borgmatic 1.8.11

• #815: Add optional Healthchecks auto-provisioning via "create_slug" option.
• #851: Fix lack of file extraction when using "extract --strip-components all" on a path with a
  leading slash.
• #854: Fix a traceback when the "data" consistency check is used.
• #857: Fix a traceback with "check --only spot" when the "spot" check is unconfigured.