Store a target's settings as columns (closes #543)

A target's settings move from the per-type JSON string in
targets.config to columns: url, headers, timeout_seconds,
forward_query, archive_expiry and archive_rotation. A column a type
does not use stays empty. headers holds the header map as JSON text
through GORM's JSON serializer, and archive_expiry holds a
time.Duration, 0 meaning never. The forms check each setting once,
with the same refusals and messages, and the edit form is filled from
the columns, so the per-type config structs, their parsers and the
"could not be read" branches are gone. A delivery task carries the
six settings in place of the JSON string; tests check that each copy
into a task, and back out of one, keeps all six.

Model: opus-5-5

internal/delivery/event_db_isolation_test.go

@@ -69,7 +69,6 @@ func TestEventDBHoldsNoTargetRows(t *testing.T) {
 	))
 	defer ts.Close()
 
-	cfg := iHTTPConfig(ts.URL)
 	targetID := uuid.New().String()
 	dbPath := s.DBMgr.DBPath(s.WebhookID)
 
@@ -85,7 +84,7 @@ func TestEventDBHoldsNoTargetRows(t *testing.T) {
 	)
 	task := iTask(
 		d, event, s.WebhookID, targetID,
-		"leaky-target", cfg, 5, 1, &body,
+		"leaky-target", ts.URL, 5, 1, &body,
 	)
 
 	s.Engine.ExportProcessNewTask(context.TODO(), &task)
@@ -102,7 +101,7 @@ func TestEventDBHoldsNoTargetRows(t *testing.T) {
 	// https://git.eeqj.de/sneak/webhooker/issues/107.
 	iCreateTarget(
 		t, s.MainDB, targetID, s.WebhookID, "leaky-target",
-		database.TargetTypeHTTP, cfg, 5,
+		database.TargetTypeHTTP, ts.URL, 5,
 	)
 
 	rd := iSeedDelivery(
@@ -111,7 +110,7 @@ func TestEventDBHoldsNoTargetRows(t *testing.T) {
 	)
 	rTask := iTask(
 		rd, event, s.WebhookID, targetID,
-		"leaky-target", cfg, 5, 2, &body,
+		"leaky-target", ts.URL, 5, 2, &body,
 	)
 
 	s.Engine.ExportProcessRetryTask(context.TODO(), &rTask)
@@ -138,7 +137,6 @@ func TestEventDBHoldsNoTargetRowsOnFailedDelivery(t *testing.T) {
 	))
 	defer ts.Close()
 
-	cfg := iHTTPConfig(ts.URL)
 	targetID := uuid.New().String()
 
 	event := iSeedEvent(
@@ -152,7 +150,7 @@ func TestEventDBHoldsNoTargetRowsOnFailedDelivery(t *testing.T) {
 	)
 	task := iTask(
 		d, event, s.WebhookID, targetID,
-		"leaky-target", cfg, 1, 1, &body,
+		"leaky-target", ts.URL, 1, 1, &body,
 	)
 
 	s.Engine.ExportProcessNewTask(context.TODO(), &task)