INT-3367: Add `GemfireMetadataStore`

JIRA: https://jira.spring.io/browse/INT-3367

INT-3367 Polishing

Rename test class; move to metadata package; doc polishing.
INT-2975: Add `ValueExpression` for typed SpEL

JIRA: https://jira.spring.io/browse/INT-2975
INT-2975: Add `type` attr. for enricher property
INT-2975: Check for `type`, polishing, docs