This change introduces a new option, [healthcheck] enabled, which
enables the healthcheck middleware in mistral-api pipeline.
This middleware allows status check at /healthcheck path, which is
useful for load balancers or any monitoring services to validate health
of its backend services.
This change is created based on the same change proposed to ironic[1].
[1] 6f439414bdcef9fc02f844f475ec798d48d42558
Co-Authored-By: Jim Rollenhagen <jim@jimrollenhagen.com>
Change-Id: I9bf3de8a5ae6a8c9346285147732b773a3667f7e