Add hint when hypertable creation fails

When creating a hypertable, we create default indexes on the partition
column, which requires that the column be a part of the table's primary
or composite key. The error message shown to the user in this scenario
did not indicate this correctly. This adds a hint to make this clearer.

Closes #2907.

.unreleased/pr_7565

@@ -0,0 +1,2 @@
+Implements: #7565 Add hint when hypertable creation fails
+Thanks: @k-rus for suggesting the improvement

src/indexing.c

@@ -95,8 +95,8 @@ ts_indexing_verify_columns(const Hyperspace *hs, const List *indexelems)
 			ereport(ERROR,
 					(errcode(ERRCODE_TS_BAD_HYPERTABLE_INDEX_DEFINITION),
 					 errmsg("cannot create a unique index without the column \"%s\" (used in "
-							"partitioning)",
-							NameStr(dim->fd.column_name))));
+							"partitioning)", NameStr(dim->fd.column_name)),
+					 errhint("If you're creating a hypertable on a table with a primary key, ensure the partitioning column is part of the primary or composite key.")));
 	}
 }