Example user jar for iterators

[patchwork01]

Background

Required for:

• System test user jars in ingest, compaction and query #4134

Description

We'd like to build an example jar containing iterator implementations to be applied during ingest, during queries or against a table for compaction.

This should be suitable for testing the system, either manually or by a future automated system test.

Analysis

There are some example iterator classes already in the core module in the package sleeper.core.iterator.impl. We could move them to their own module and build a fat jar for that module. We can copy that jar over to the built jars directory in scripts/build/buildForTest.sh.

We can then test it in AWS in a manual system test instance. We can manually upload the jar to the jars bucket, and set it as a user jar in the instance properties.