Add support for foreign keys to hypertables

Currrently we only allow Hypertables references other tables, with
this patch the opposite direction is supported as well and tables
can have foreign key references into hypertables.

src/CMakeLists.txt

@@ -21,6 +21,7 @@ set(SOURCES
     extension.c
     extension_constants.c
     expression_utils.c
+    foreign_key.c
     gapfill.c
     guc.c
     histogram.c

src/chunk_constraint.c

@@ -33,6 +33,7 @@
 #include "dimension_vector.h"
 #include "errors.h"
 #include "export.h"
+#include "foreign_key.h"
 #include "hypercube.h"
 #include "hypertable.h"
 #include "partitioning.h"
@@ -512,6 +513,9 @@ ts_chunk_constraints_create(const Hypertable *ht, const Chunk *chunk)
 		Assert(list_length(cookedconstrs) == list_length(newconstrs));
 		CommandCounterIncrement();
 	}
+
+	/* Copy FK triggers to this chunk */
+	ts_chunk_copy_referencing_fk(ht, chunk);
 }
 
 ScanIterator