Add basic synchronous API for triggering reconcilation runs

[chadlwilson]

Context / Goal

To support performance testing it would be useful to have a basic API to trigger a reconcilation run, and wait for it to be complete.

This way, when implementing #26 we can use simple timed HTTP calls. Ideally the response can tell us various timings that we can use for reporting purposes.

Expected Outcome

• Add an HTTP/JSON REST API that
  • allows a rec run to be triggered by identifier against a pre-configured source and target DB with pre-configured queries
  • reports the results of the rec run back to the user synchronously

Out of Scope

• Creating a truly async API from an HTTP perspective using events/websockets/polls etc. With reactive programming on source/target side, we can probably make this work just fine without anything more complex at this stage.
• Worrying about API docs or anything too fancy at this stage.

Additional context / implementation notes

[chadlwilson]

Basic API added. Paths need changing, but runs can be triggered with

echo '{ "datasetId": "test-dataset" }' | http POST http://localhost:8080/runs

Returning

{
    "completedDurationSeconds": 2.7854958,
    "completedTime": "2021-10-25T14:30:10.290869700Z",
    "createdTime": "2021-10-25T14:30:07.505373900Z",
    "datasetId": "test-dataset",
    "id": 29,
    "results": {
        "sourceRows": 1003,
        "targetRows": 1003
    }
}