add scroll-past-bottom configuration option

with gui.scrollPastBottom option true, lazygit let user scroll past the
bottom - which is default
if option is false, user cannot scroll further when bottom of file has
appeared in mainView

docs/Config.md

@@ -6,6 +6,7 @@
   gui:
     # stuff relating to the UI
     scrollHeight: 2 # how many lines you scroll by
+    scrollPastBottom: true # enable scrolling past the bottom
     theme:
       activeBorderColor:
         - white

pkg/config/app_config.go

@@ -214,6 +214,7 @@ func GetDefaultConfig() []byte {
 		`gui:
   ## stuff relating to the UI
   scrollHeight: 2
+  scrollPastBottom: true
   theme:
     activeBorderColor:
       - white

pkg/gui/gui.go

@@ -130,7 +130,12 @@ func (gui *Gui) scrollUpMain(g *gocui.Gui, v *gocui.View) error {
 func (gui *Gui) scrollDownMain(g *gocui.Gui, v *gocui.View) error {
 	mainView, _ := g.View("main")
 	ox, oy := mainView.Origin()
-	if oy < len(mainView.BufferLines()) {
+	y := oy
+	if !gui.Config.GetUserConfig().GetBool("gui.scrollPastBottom") {
+		_, sy := mainView.Size()
+		y += sy
+	}
+	if y < len(mainView.BufferLines()) {
 		return mainView.SetOrigin(ox, oy+gui.Config.GetUserConfig().GetInt("gui.scrollHeight"))
 	}
 	return nil