Add a new type to use for building filter predicates for API requests,
replacing "./api/types/filters".Args in the client. Remove the now
unused api/types/filters package.
Signed-off-by: Cory Snider <csnider@mirantis.com>
This package was originally internal, but was moved out when BuildKit
used it for its integration tests. That's no longer the case, so we
can make it internal again.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
