This adds a new tool, `health-checker`, which is a client of the new
Health Checker Service that has been integrated into all of our
boulder components. This tool takes an address, a timeout, and a
config file. It then attempts to connect to a gRPC Health Service at
the given address, retrying until it hits its timeout, using credentials
specified by the config file.
This is then wrapped by a new function `waithealth` in our Python
helpers, which serves much the same function as `waitport`, but
specifically for services which surface a gRPC Health Service
This in turn requires slight modifications to `startservers`, namely
specifying the address and port on which each service starts its
gRPC listener.
Finally, this change also introduces new credentials for this
health-checker, and adds those credentials as a valid client to
all services' json configs. A similar change would have to be made
to our production configs if we were to establish a long-lived
health checker/prober in prod.
Fixes#5074
3666322817