Get rid of initializeDb or fix it

[pkarw]

Related to #327
Wev'e got pretty cool feature of passing the db object to any middleware in the api: https://github.com/DivanteLtd/vue-storefront-api/blob/589bb876fd32077124f82d7e0ded67d440ff7129/src/index.ts#L35-L36

... which is not being used because initializeDb does nothing.
Would be super cool to pass something like:

db.redisClient
db.elasticClient

or maybe safer:

db.getRedisClient()
db.getElasticClient() - to make sure that initializeDb is not connecting/executing any queries on it's own; it should be lazy connected as most of the endpoints doesn't really need any connection to Redis and Elasitc in the end ..