When getting the start and end times, use the d3 time scale `ticks` function to round the start and end times.

Example from a query:

Before:

```json
{
          "range": {
            "@timestamp": {
              "gte": 1611262874814,
              "lte": 1611263774814,
              "format": "epoch_millis"
            }
          }
        },
```

After:

```json
{
          "range": {
            "@timestamp": {
              "gte": 1611263040000,
              "lte": 1611263880000,
              "format": "epoch_millis"
            }
          }
        },
```

The `ticks` function makes it so the amount of rounding is proportional to the size of the time range, so shorter time ranges will be rounded less.

Also fix a bug where invalid ranges in the query string were not handled correctly.

Fixes elastic#84530.