Addition of the article sharded table

[frouioui]

Adding the article table to the region-based sharded cluster could be a good direction to take. We have multiple choices, either create a whole new key-space e.g. "articles", or add the article table to the users key-space, which will require to change name. Both options have to be considered, the first one seeming (for now) better in terms of scalability.

Articles will be fragmented depending on their category, for now we have 3 categories, 2 categories are located in 2 separated shards, but the 3rd category is supposed to be replicated across the 2 initial shards, which could potentially be an issue regarding the architecture of Vitess, some research needs to be done on the replication system of Vitess before moving forward.