[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/packagemanager/apt.go

@@ -46,6 +46,9 @@ func (a *Apt) Packages() packagemap {
 		"docker": []*Package{
 			{Name: "docker.io", SystemPackage: true, Optional: true},
 		},
+		"nsis": []*Package{
+			{Name: "nsis", SystemPackage: true, Optional: true},
+		},
 	}
 }