In 2.2.0, @ConfigurationPropertiesScan was enabled by default.
Unfortunately, this had the unexpected side-effect of breaking
conditional enablement of a @ConfigurationProperties class via
@EnableConfigurationProperties if the @ConfigurationProperties class
was in a package covered by scanning.

This commit remove @ConfigurationPropertiesScan from
@SpringBootApplication so that it is no longer enabled by default.
2.1.x users who rely upon such conditional enablement of
@ConfigurationProperties classes can now upgrade to 2.2.x without
having to make any changes. Users who do not have such a need and are
in a position to use configuration properties scanning can now opt-in
by adding @ConfigurationPropertiesScan to their main application class
alongside @SpringBootApplication.

Closes gh-18674