Support configure code-only configuration for StackExchange.Redis bus

[Memoyu]

Usage:

var redisConfig = ConfigurationOptions.Parse("127.0.0.1:6379");
redisConfig.DefaultDatabase = 6;
services.AddEasyCaching(option =>
{
    option.WithRedisBus(config =>
    {
        config.ConfigurationOptions = redisConfig;
        config.SerializerName = "myredis";
    });
});

[catcherwong]

LGTM