Allow users to be able to run assert (data tests) on specific models

[DylanBaker]

Currently, the assert command runs all data tests. It appears from the docs that we could specific which models it should run. We should allow that workflow.

It appears that you can't specify this at an explore level via the run API endpoint, but it's possible the explore is attached to the returned data in the 'Get All LookML' tests endpoint and that we could filter from there and specify exactly which tests we want to run.

[DylanBaker]

The get all lookml tests endpoint does return the explores, so we should actually be able to provide the same model selection syntax as we do for the SQL validator.

Example response:

[
  {
    "model_name": "jaffle_shop",
    "name": "historic_revenue_is_accurate",
    "explore_name": "fct_orders",
    "query_url_params": "fields=fct_orders.count_orders&f[fct_orders.order_year]=2018&limit=500&dynamic_fields=%5B%7B%22table_calculation%22%3A%22looker_assert_revenue_is_expected_value%22%2C%22label%22%3A%22Revenue+Is+Expected+Value%22%2C%22expression%22%3A%22%24%7Bfct_orders.count_orders%7D+%3D+99+%22%7D%5D",
    "file": "jaffle_shop/jaffle_shop.model.lkml",
    "line": 14,
    "can": {}
  }
]