Fix for ELE-699, None default for --group-by

[RoiTabach]

Copied from CR 819 to make the automation work

[linear]

ELE-699 group_alerts_by in config.yml not respected

Describe the bug
The group_alerts_by value in config.yml is not respected because the option has a default value of alerts.

elementary/elementary/monitor/cli.py

Lines 217 to 222 in 2bc0204

	@click.option(
	"--group-by",
	type=click.Choice(["alert", "table"]),
	default="alert",
	help="Whether to group alerts by 'alert' or by 'table'",
	)

So eventually when the Config is instantiated, the self.slack_group_alerts_by gets the default value that is first and not the config value.

elementary/elementary/config/config.py

Lines 111 to 115 in 2bc0204

	self.slack_group_alerts_by = self._first_not_none(
	slack_group_alerts_by,
	slack_config.get("group_alerts_by"),
	GroupingType.BY_ALERT.value,
	)

To Reproduce
Steps to reproduce the behavior:

1. Setup config.yml with group_alerts_by: "table"
2. Run edr monitor
3. Check in Slack that the alerts are not grouped by table

Expected behavior
My expectations were:

• for the command to run using the config value of group_alerts_by
• for the Slack alerts to be grouped by table

Environment (please complete the following information):

• edr Version: 0.7.7
• dbt package Version: 0.7.5

Additional context
My proposal is to make the default value in click.option to be None, since later the alert is the default fallback.

I can create a PR if you'd like.

[github-actions]

👋 @RoiTabach
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