Run all Rails tests in sharded mode

[deepthi]

2 shards should be sufficient.
This will require specifying a vschema for all the tables being created.
VSchema can be created by executing DDLs as documented here.

[Akilan1999]

Me and @GuptaManan100 had a discussion:

• We are planning to use a variable called $NUM_SHARDS as the Vitess docker image takes that as an argument
• We will use VSchema queries from the bash script (If we are running in sharded mode) .

[deepthi]

Sounds like a good plan 👍

[GuptaManan100]

The addition of the Active Record Migration guide is at #127
The addition of the Active Record Validation guide is at #144
The addition of the Active Record Callbacks and Associations guides are at #146
The addition of the Active Record Query Interface guide is at #147