implement edge dictionary injectable for testing process

[ysugimoto]

Fixes #404

This PR implements injectable edge dictionary as a table declaration on testing process like simulator configuration.

Configuration

We will define the config.testing.edge_dictionary as the same as config.simulator.edge_dictionary.
Once I thought that we can use config.simulator.edge_dictionary also in the testing process but I decided that the simulator and testing should work independenctly so I divided configuration.

...
testing:
  edge_dictionary:
    foo:
      some: value
...

Changes

And I added a tiny improvement, We only can override dictionary items for existing table, but now we can also inject the edge dictionary as a new table declaration.
This makes the user can inject any edge dictionary even not defined in main VCL (or Fastly Service) - it's better performace for testing because we don't need to fetch the remote edge dictionary - but need to take care that the main VCL will have dependency to the injected dictionary.
Please make sure the tests should pass without dictionary injection before deployments.