lib/ur: Implement crash (panic) reporting (fixes #959) (#5702)

* lib/ur: Implement crash (panic) reporting (fixes #959)

This implements a simple crash reporting method. It piggybacks on the
panic log files created by the monitor process, picking these up and
uploading them from the usage reporting routine.

A new config value points to the crash receiver base URL, which defaults
to "https://crash.syncthing.net/newcrash" (following the pattern of
"https://data.syncthing.net/newdata" for usage reports, but allowing us
to separate the service as required).

lib/config/config_test.go

@@ -69,6 +69,8 @@ func TestDefaultValues(t *testing.T) {
 		UnackedNotificationIDs:  []string{},
 		DefaultFolderPath:       "~",
 		SetLowPriority:          true,
+		CRURL:                   "https://crash.syncthing.net/newcrash",
+		CREnabled:               true,
 		StunKeepaliveStartS:     180,
 		StunKeepaliveMinS:       20,
 		StunServers:             []string{"default"},
@@ -203,7 +205,8 @@ func TestOverriddenValues(t *testing.T) {
 		ProgressUpdateIntervalS: 10,
 		LimitBandwidthInLan:     true,
 		MinHomeDiskFree:         Size{5.2, "%"},
-		URSeen:                  2,
+		URSeen:                  8,
+		URAccepted:              4,
 		URURL:                   "https://localhost/newdata",
 		URInitialDelayS:         800,
 		URPostInsecurely:        true,
@@ -211,15 +214,14 @@ func TestOverriddenValues(t *testing.T) {
 		AlwaysLocalNets:         []string{},
 		OverwriteRemoteDevNames: true,
 		TempIndexMinBlocks:      100,
-		UnackedNotificationIDs: []string{
-			"channelNotification",   // added in 17->18 migration
-			"fsWatcherNotification", // added in 27->28 migration
-		},
-		DefaultFolderPath:   "/media/syncthing",
-		SetLowPriority:      false,
-		StunKeepaliveStartS: 9000,
-		StunKeepaliveMinS:   900,
-		StunServers:         []string{"foo"},
+		UnackedNotificationIDs:  []string{"asdfasdf"},
+		DefaultFolderPath:       "/media/syncthing",
+		SetLowPriority:          false,
+		CRURL:                   "https://localhost/newcrash",
+		CREnabled:               false,
+		StunKeepaliveStartS:     9000,
+		StunKeepaliveMinS:       900,
+		StunServers:             []string{"foo"},
 	}
 
 	os.Unsetenv("STNOUPGRADE")