Fix platform requirements (#214)

- Replace the placeholder platform requirements with `@available(macOS 12, iOS 15, tvOS 15, watchOS 8, *)` 
- Bump required dependency versions: `swift-nio`, `swift-log` and `swift-backtrace`

Author: fabianfett

Package.swift

@@ -15,9 +15,9 @@ let package = Package(
         .library(name: "AWSLambdaTesting", targets: ["AWSLambdaTesting"]),
     ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-nio.git", .upToNextMajor(from: "2.28.0")),
-        .package(url: "https://github.com/apple/swift-log.git", .upToNextMajor(from: "1.0.0")),
-        .package(url: "https://github.com/swift-server/swift-backtrace.git", .upToNextMajor(from: "1.1.0")),
+        .package(url: "https://github.com/apple/swift-nio.git", .upToNextMajor(from: "2.30.0")),
+        .package(url: "https://github.com/apple/swift-log.git", .upToNextMajor(from: "1.4.2")),
+        .package(url: "https://github.com/swift-server/swift-backtrace.git", .upToNextMajor(from: "1.2.3")),
     ],
     targets: [
         .target(name: "AWSLambdaRuntime", dependencies: [