Previously, the Spring Boot plugin would automatically apply the
dependency management plugin and import the spring-boot-dependencies
bom. This made it very difficult to use Spring Boot's plugin without
also using its dependency management. It also made it difficult to
see where the dependency management was coming from.
This commit updates the Spring Boot plugin so that it no longer
automatically applies the dependency management plugin. Instead, the
plugin now reacts to the dependency management plugin being applied
by importing the spring-boot-dependencies bom. Users that do not
wish to use Spring Boot's dependency management capabilities can now
do so by not applying the dependency management plugin.
Closes gh-3164
b1f9123311