Make compiler plugin work in samples (for docs)

[Jolanrensen]

As a follow-up for #1414 @AndreiKingsley tried to enable the compiler plugin in :tests :samples.
This fails currently because the compiler plugin expects the jar of :core/:dataframe-compiler-plugin-core on the classpath.

Currently, this is not the case, as we depend on the module, not the released version; the jar.

We could use a tactic I came up with for kotlin-spark:

• We create a gradle task that runs the jar-task on each build and copies the jar into a separate directory
• And depend on it from the examples project, like here and here