Use spring.build-type to control the Gradle conventions' behavior

[wilkinsona]

It would be useful to be able to control the conventions' behavior depending on what we're building. For example, a plain OSS build should behave as it does today but when we're working on a CVE fix, we may not want to publish a build scan to eliminate the risk of leaking information about the vulnerability in the branch name, test method names, etc.

We can achieve this with Gradle through a property in gradle.properties (we'll have to read the file manually, but that should be good enough). It's not clear what we should do with Maven as I can't find any details on how to configure an extension using properties or similar. We'll tackle the Maven side of things later, perhaps using a separate file or the like.

[wilkinsona]

Closed by 39c4e68.