Issue title: [ISSUE] databricks_job new_cluster aws_attributes requires zone_id when instance_pool_id configured
 Issue body: ### Terraform Version

Terraform v0.12.28
+ provider.databricks v0.2.3

### Affected Resource(s)

- databricks_job

### Terraform Configuration Files
```hcl
resource "databricks_job" "ingest_all" {
  name = "foo"
  notebook_path = "foo/Ingest All"
  new_cluster {
    spark_version = "7.0.x-scala2.12"
    instance_pool_id = databricks_instance_pool.curator.id
    autoscale {
      min_workers = 2
      max_workers = 8
    }
    aws_attributes {
      instance_profile_arn = databricks_instance_profile.curator.instance_profile_arn
    }
    custom_tags = {
      product = "curator"
    }
  }
  max_concurrent_runs = 1
  max_retries = 0
  timeout_seconds = 0
  schedule {
    quartz_cron_expression = "0 0 */12 * * ?"
    timezone_id = "US/Pacific"
  }
}
```

### Debug Output

```
Error: Missing required argument

  on main.tf line 134, in resource "databricks_job" "ingest_all":
 134:     aws_attributes {

The argument "zone_id" is required, but no definition was found.
```

### Expected Behavior

When instance_pool_id is given, zone_id is not required.  Extra aws_attributes should not be added.

### Actual Behavior

Complains about missing argument.

If zone_id is actually set however, then the generated plan includes:

```
          + aws_attributes {
              + availability           = "SPOT_WITH_FALLBACK"
              + instance_profile_arn   = "arn:aws:iam38d1:d2b4:3d06:83e8:96a5:8c2:893d:aba5....REDACTED"
              + spot_bid_price_percent = 100
              + zone_id                = "us-east-1f"
            }
```

Which is also invalid, as availability and spot_bid_price_percent should not be set with an instance_pool IIUC.

 Comments: 
 Comment 0: Fixed on master branch
{'source': 'GithubIssues', 'repo_name_with_owner': 'databrickslabs/terraform-provider-databricks', 'issue_id': 657672401, 'repo_stars': 191.0}