Spring Boot Admin Integration enhancements

[TimHess]

ConfigurationUrlHelpers should move to a more centralized location so they can also be used for registering with Spring Boot Admin.

Consider adding extension(s) for program.cs and/or including with general actuator setup for a more polished experience.

[bart-vmware]

Currently (main), the code first looks for spring:boot:admin:client:basePath in configuration, then falls back to using the hostname in the bound ASP.NET listen addresses (unlikely to find it there), then fails with an error.

Eureka uses several strategies for determining the hostname, we should explore if we can borrow from it.