[v2] NSIS installer support for Windows (#1184)

* [v2] Add support for post build hooks

Currently only supports build-level hooks

* [v2] Improve build assets handling and use single source for manifest generation

The manifest asset files are now a go template and data will be
resolved before they are included into the build output.

Breaking Change: Windows manifest file must be named
“wails.exe.manifest” and doesn’t depend on the project name
anymore.

* [v2, windows] NSIS installer generation

v2/internal/system/system.go

@@ -1,10 +1,11 @@
 package system
 
 import (
-	"github.com/wailsapp/wails/v2/internal/system/operatingsystem"
-	"github.com/wailsapp/wails/v2/internal/system/packagemanager"
 	"os/exec"
 	"strings"
+
+	"github.com/wailsapp/wails/v2/internal/system/operatingsystem"
+	"github.com/wailsapp/wails/v2/internal/system/packagemanager"
 )
 
 var (
@@ -75,6 +76,28 @@ func checkUPX() *packagemanager.Dependancy {
 	}
 }
 
+func checkNSIS() *packagemanager.Dependancy {
+
+	// Check for nsis installer
+	output, err := exec.Command("makensis", "-VERSION").Output()
+	installed := true
+	version := ""
+	if err != nil {
+		installed = false
+	} else {
+		version = strings.TrimSpace(strings.Split(string(output), "\n")[0])
+	}
+	return &packagemanager.Dependancy{
+		Name:           "nsis ",
+		PackageName:    "N/A",
+		Installed:      installed,
+		InstallCommand: "Available at https://nsis.sourceforge.io/Download",
+		Version:        version,
+		Optional:       true,
+		External:       false,
+	}
+}
+
 func checkDocker() *packagemanager.Dependancy {
 
 	// Check for npm