Add caching to enrichment service calls

Enrichment services usually call paid external services, eg. AWS Comprehend. I noticed from the translation implementation that a cache would be useful to avoid unnecessary calls. e.g. the following call could be cached.

["{'source':'en','target':'es','text':'I am very disappointed','translated':'Estoy muy decepcionado.'}"]

If we implement a generic cache in AbstractEnrichmentService, any enrichment implementation could benefit from it.