Provide build time external resource

When we build a project, we have faced certain corner cases where a build time external resource is required (see #4200). We've recently worked on the possibility to alter the maven build by changing the settings (#4568), so we may try to use the same approach and develop a feature where the user can include any resource to be considered at build time.

For example:
```
-t builder.resource=configmap:my-file.txt
```
would include the resource in the classpath for any build time need.

Start by reviewing the approaches referenced in issues #4200 and #4568, especially how Maven build settings are altered. Define how the `builder.resource=configmap:my-file.txt` input should make an external resource available on the build-time classpath, and verify that arbitrary supported resources are included during a build.

Written by the indexing model from the issue text.