Add DB option to RedisAdapterOptions

[ezerozen]

Add DB option to RedisAdapterOptions for specifies the database in redis.Dial

[sshaplygin]

@ezerozen Hey, Ezequiel! Thank you so match for your PR!

What's happened if we don't set DB options at the redis connection?

[sshaplygin]

LGTM

[ezerozen]

@ezerozen Hey, Ezequiel! Thank you so match for your PR!

What's happened if we don't set DB options at the redis connection?

@sshaplygin If we don't set DB options it use the default database (0).

Redis databases are numbered from 0 to 15 and, by default, you connect to database 0 when you connect to your Redis instance. However, you can change the database you’re using with the select command after you connect.

If you set any database number greater 0, the client execute the select command:
https://github.com/gomodule/redigo/blob/d6854479365f0307560fa28e18e2bd0634b05229/redis/conn.go#L307-L312