Add request handlers to AWS clients

[akefirad]

Type: Feature

Description
Currently it's impossible to customize clients created by AmazonWebserviceClientFactoryBean, specifically by adding RequestHandler2 (for example tracing instrumentation handler).

Solution
The class should accept a list of request handlers and add them before building the client.

Alternatives
At the very least, I'd like to have access to the builder before calling the factory calls builder.build() (e.g. overrider the createInstance method's behavior.).

Additional context
If you wish to accept this, I'd be happy to send a PR.

[maciejwalkowiak]

@akefirad that's a very good idea. Lets keep it for 3.0 version, where we are based on AWS SDK v2.

[MatejNedic]

I think we can close this one since it is supported by AwsClientCustomizer