Add a meta_caches system table for viewing configured metadata caches

[hiltontj]

There will be a system table that can be queried via:

SELECT * FROM system.meta_caches WHERE table = 'cpu'

The table predicate is required. This will return results with columns for:

• table the cache's target table name
• name the name of the cache
• column_ids as a list of ColumnIds, that the cache is configured on
• column_names as a list of the column's names, that the cache is configured on
• max_age or null if it is not configured for the cache