[Feature Request] Add schema check for config file

[ybiquitous]

To save Querly users from typos on querly.yml, I strongly suggest checking the schema of querly.yml.

For example, because I couldn't notice a typo like except and expect, my configuration (rule2) didn't work well. 😓

check:
  - path: /
    rules:
      - except: rule1
      - expect: rule2

When there are mistakes in the configuration like above, I hope querly check or querly test command fails immediately and outputs an easy message to understand.

For example:

$ querly test
Error: Querly configuration in /path/to/my/project/querly.yml is invalid:
       - Unexpected property "expect".

What do you think about this suggestion?