So far we have wrongly advertized that the `spring-boot-starter-parent`
filters application configuration in such a way that standard Spring
placeholders are not processed.

In order to achieve such feature, the `useDefaultDelimiters` property
must be set to `false` as otherwise default delimiters are appended to
the list of custom delimiters.

This property is not enabled so that only keys surrounded by `@` are
filtered by the build.

Closes gh-3092