Allow stream_name configuration value to be a callable

[fish3046]

This implements a helpful feature for me and my team. The requirements:

1. Have two different Cloudwatch log streams, one for web traffic and one for background worker traffic
2. Have config:cache executed on production

I had something like 'stream_name' => app()->runningInConsole() ? 'laravel-worker' : 'laravel' in the config, but cache:config would process this and always end up as laravel-worker, even for web traffic.

This feature would let you do things like 'stream_name' => [CallableStreamNameGenerator::class, 'generateStreamName'] to fetch the stream name at run time.