[BUG][data-prepper] Empty objects pruned during helm values merge

[janhoy]

Describe the bug
Some sample values in helm chart's values file define empty object implicitly by a dangling colon:

      source:
        random:

While this works for a plain helm install, it will crash when using override values since the yaml merge will think it is an empty useless object and prune it, causing source: {}. To avoid this, be explicit about the empty object:

      source:
        random: {}

I believe the simple-sample-pipeilne should not be in default values at all (see #624 ), but no matter where the sample pipeline is referenced (chart, documentation, website), it should use the best practice of explicitly defining the empty object.

To Reproduce
Steps to reproduce the behavior:

1. Install the helm chart with a simple override values file that do not touch the pipelineConfig at all
2. Watch the secret contains an empty source and pipeline fails due to lack of configured source.

Expected behavior
Expected the random source not to be lost at helm install.

Chart Name
data-prepper

[prudhvigodithi]

[Triage]
Thanks for the contribution @janhoy, adding @TheAlgo @peterzhuamazon to please take a look.