This commit adds the new "`spring.main.cloud-platform`" configuration
property. This allows applications to override the auto-detection and
force a specific Cloud Platform. This is useful for testing behavior on
a local machine or force the detection of a particular platform.

This commit also adds a new `CloudPlatform.NONE` value that allows
applications to disable the auto-detection of the Cloud Platform, thus
avoiding issues with false positives.

Closes gh-20553