feat(lagoon): per-query collation for OrderBy, drop the database locale check

- lagoon.OrderBy takes variadic lagoon.OrderOption values; lagoon.Collate(name)
  emits a validated, double-quoted COLLATE clause (e.g. "pl-x-icu")
- remove the exported CheckLocale and the ICU pl-PL check from Open and Use
- framework test containers and per-test databases are plain PostgreSQL
- lagoon README, root README and docs pages drop the locale requirement;
  queries-and-pagination gains a "Sorting with a collation" section
  backed by ExampleCollate

modules/lagoon/postgres_test.go

@@ -55,9 +55,6 @@ func startLagoonPostgres(ctx context.Context) error {
 		postgres.WithUsername("lagoon"),
 		postgres.WithPassword("lagoon"),
 		postgres.BasicWaitStrategies(),
-		testcontainers.WithEnv(map[string]string{
-			"POSTGRES_INITDB_ARGS": "--locale-provider=icu --icu-locale=pl-PL --encoding=UTF8",
-		}),
 	)
 	if err != nil {
 		return err
@@ -108,7 +105,7 @@ func dedicatedDB(t *testing.T, name string) (*sql.DB, string) {
 	admin := lagoonDB(t)
 	ctx := t.Context()
 	quoted := `"` + strings.ReplaceAll(name, `"`, `""`) + `"`
-	if _, err := admin.ExecContext(ctx, `CREATE DATABASE `+quoted+` TEMPLATE template0 ENCODING 'UTF8' LOCALE_PROVIDER icu ICU_LOCALE 'pl-PL'`); err != nil && !strings.Contains(err.Error(), "already exists") {
+	if _, err := admin.ExecContext(ctx, `CREATE DATABASE `+quoted+` TEMPLATE template0 ENCODING 'UTF8'`); err != nil && !strings.Contains(err.Error(), "already exists") {
 		t.Fatalf("create %s: %v", name, err)
 	}
 	dsn, err := dsnWithDB(lagoonDSN, name)