config init now leaves out the test sources unless given --all

A section tagged init:"hidden" isn't written to the file config init
generates; fts_mock and sleeper are. config init --all writes them too.
They still load, and the config commands read and set them as before.

internal/config/conf_sections_test.go

@@ -288,6 +288,26 @@ func TestConcreteSourceSections(t *testing.T) {
 	}
 }
 
+// InitDefaults leaves out the sections tagged init:"hidden" unless asked.
+func TestInitDefaults(t *testing.T) {
+	all := InitDefaults(true)
+	shown := InitDefaults(false)
+	if all["sources.sleeper.enabled"] != false ||
+		all["sources.fts_mock.interval"] != "10m0s" {
+		t.Errorf("all = %v; want the test sources' defaults", all)
+	}
+	for key := range all {
+		hidden := strings.HasPrefix(key, "sources.fts_mock.") ||
+			strings.HasPrefix(key, "sources.sleeper.")
+		if _, found := shown[key]; found == hidden {
+			t.Errorf("%s: in the generated defaults = %v", key, found)
+		}
+	}
+	if shown["sources.eu_supply.base_url"] != "https://uk.eu-supply.com" {
+		t.Errorf("eu_supply missing: %v", shown)
+	}
+}
+
 func TestEUSupplySection(t *testing.T) {
 	conf := defaultConfig(t)
 	got := conf.Sources.EUSupply