Refactor SummaryMetadataEnricher for improved readability

[zbqmgldjfh]

We've used methods throughout the code to give it meaning.
The old code was very hard to read because you had to read so many implementations.

You can definitely see the improvement in readability after refactoring.

The test was performed using the MetadataTransformerIT class.

[markpollack]

I think this refactoring goes a bit too far for my taste, it decomposes it too much and passing around the index makes it more confusing. I've made a small change

		for (int i = 0; i < documentSummaries.size(); i++) {
			Map<String, Object> summaryMetadata = getSummaryMetadata(i, documentSummaries);
			documents.get(i).getMetadata().putAll(summaryMetadata);
		}

in this commit 7775a76 as i think this helps with clarity.

Thanks for the PR and sorry it took so long to get around to it.