[Scala-Akka-Http] `ActorMaterializer` is deprecated

Description

openapi-generator version

5.3.0

OpenAPI declaration file content or url

Any

Command line used for generation

Steps to reproduce

1. Generate any open api spec with the Scala Akka HTTP client generator
2. Notice that the ApiInvoker.scala uses the deprecated ActorMaterializer that has been deprecated since akka-http 2.6.0.

ApiInvoker.scala:94:58
[E]      method apply in object ActorMaterializer is deprecated (since 2.6.0): Use the system wide materializer with stream attributes or configuration settings to change defaults
[E]      L94:   private implicit val materializer: ActorMaterializer = ActorMaterializer()
ApiInvoker.scala:94:38
[E]      class ActorMaterializer in package stream is deprecated (since 2.6.0): The Materializer now has all methods the ActorMaterializer used to have
[E]      L94:   private implicit val materializer: ActorMaterializer = ActorMaterializer()

Related issues/PRs

Suggest a fix/enhancement

We should change the invoker template to use Materializer(system)

https://github.com/OpenAPITools/openapi-generator/blob/5a62ae6628fb30d2fd61c42c8d1961614ea757f1/modules/openapi-generator/src/main/resources/scala-akka-client/apiInvoker.mustache#L84

Start with modules/openapi-generator/src/main/resources/scala-akka-client/apiInvoker.mustache around line 84 and inspect how the Scala Akka HTTP client creates its materializer. Generate a client from any OpenAPI specification and verify that ApiInvoker.scala uses Materializer(system) without the reported ActorMaterializer deprecation warnings.