[Tests] Add an integration test product for easier iteration (#121)

[Tests] Add an integration test product for easier iteration

### Motivation

Some IDEs don't allow you to trigger building of targets, only products.

### Modifications

Added an umbrella library product to make it possible to build locally in an IDE, not just using `swift build`.

### Result

Now the product shows up in IDEs, allowing developers to iterate on the code and rebuild.

### Test Plan

Tested that it shows up locally.


Reviewed by: simonjbeaumont

Builds:
     ✔︎ pull request validation (5.8) - Build finished. 
     ✔︎ pull request validation (5.9) - Build finished. 
     ✔︎ pull request validation (docc test) - Build finished. 
     ✔︎ pull request validation (integration test) - Build finished. 
     ✔︎ pull request validation (nightly) - Build finished. 
     ✔︎ pull request validation (soundness) - Build finished. 

#121

Author: czechboy0

IntegrationTest/Package.swift

@@ -19,6 +19,18 @@ let package = Package(
     platforms: [
         .macOS(.v13)
     ],
+    products: [
+        .library(
+            name: "IntegrationTestLibrary",
+            targets: [
+                "Types",
+                "Client",
+                "Server",
+                "MockTransportClient",
+                "MockTransportServer",
+            ]
+        )
+    ],
     dependencies: [
         .package(url: "https://github.com/apple/swift-openapi-generator", .upToNextMinor(from: "0.1.0")),
         .package(url: "https://github.com/apple/swift-openapi-runtime", .upToNextMinor(from: "0.1.0")),