This change adds a healthcheck params dict to k8s charms for
use by traefik via the ingress relation. It contains a path,
interval, and timeout value. This allows traefik to detect
down nodes and remove them from the loadbalancer rotation.
Unless overridden in the charm, a default path of "/" is
passed in the ingress relation. Interval and timeout
are optional and will use default values of 30s and 5s,
respectively, unless overridden in the charm. Some charms
define a "/healthcheck" path in api-paste.ini which has been
used in place of the default "/" path.
Closes-Bug: #2077269
Change-Id: I355728f338e9a29fcf202cc629a977b49b2d8990
1f30344dbf