chore: move single-instance plugin

plugins/single-instance/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "tauri-plugin-single-instance"
+description = "Ensure a single instance of your tauri app is running."
+version = "0.0.0"
+authors = ["Tauri Programme within The Commons Conservancy"]
+license = "Apache-2.0 OR MIT"
+edition = "2021"
+rust-version = "1.60"
+exclude = ["/examples"]
+
+[dependencies]
+tauri = { version = "1" }
+
+[target.'cfg(target_os = "windows")'.dependencies.windows-sys]
+version = "0.42"
+features = [
+    "Win32_System_Threading",
+    "Win32_System_DataExchange",
+    "Win32_Foundation",
+    "Win32_UI_WindowsAndMessaging",
+    "Win32_Security",
+    "Win32_System_LibraryLoader",
+    "Win32_Graphics_Gdi",
+]
+
+[target.'cfg(target_os = "linux")'.dependencies]
+zbus = "3"