Support filtering contents of granule stores in vector mosaic stores

Allow adding a CQL filter in the granule index, to support grabbing a subset of the features in the granule store. This helps support the migration of existing databases to file-based source, with an interim period where both the old database and the new file-based sources are used (the old database is sliced into virtual granules, following the same splitting of files, until it is completely migrated away).