analyse, document and suggest indexing the JDBC cache store

Adding indexes to the JDBC cache store's backend table can drastically increase performance especially for the JdbcStringBasedCacheStore and partially for the JdbcMixedCacheStore.
Investigate weather indexes can be defined through Jdbc in a portable manner (same way the tables are created on startup) or at least update documentation to describe how indexes should be defined and the advantages of having them defined.