Implement create user

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/coredata/membership_profile.go

@@ -22,6 +22,7 @@ import (
 	"time"
 
 	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgconn"
 	"go.gearno.de/kit/pg"
 	"go.probo.inc/probo/pkg/gid"
 	"go.probo.inc/probo/pkg/mail"
@@ -904,6 +905,11 @@ VALUES (
 
 	_, err := conn.Exec(ctx, q, args)
 	if err != nil {
+		var pgErr *pgconn.PgError
+		if errors.As(err, &pgErr) && pgErr.Code == "23505" {
+			return ErrResourceAlreadyExists
+		}
+
 		return fmt.Errorf("cannot insert profile: %w", err)
 	}