Allow customizing message for Slack notifications

[nawatts]

slack_notifications uses the process name from sys.argv in notifications.

gnomad_methods/gnomad/utils/slack.py

Lines 156 to 172 in 0b8e100

	process = os.path.basename(sys.argv[0])
	try:
	yield
	slack_client = SlackClient(token)
	slack_client.send_message(
	to, f":white_check_mark: Success! {process} finished!"
	)
	except Exception as e:
	slack_client = SlackClient(token)
	slack_client.send_file(
	to,
	content=traceback.format_exc(),
	filename=f"error_{process}_{time.strftime('%Y-%m-%d_%H:%M')}.log",
	filetype="text",
	comment=f":x: Error in {process}",
	)

However, someone may want notifications about multiple blocks in the same script. There should be a way to distinguish those notifications.