SERVER-62277 Add `freeStorage` option to dbstats, off by default

jstests/core/dbstats.js

jstests/noPassthroughWithMongod/free_storage_size.js

src/mongo/db/catalog/database.h

src/mongo/db/catalog/database_impl.cpp

src/mongo/db/catalog/database_impl.h

src/mongo/db/commands/dbcommands.cpp

src/mongo/shell/db.js