Set alerting to empty dict to ensure it is disabled by default

[zhan9san]

Fix #220

If we set the variable grafana_alerting to {}, the alerting .enabled would be set to false.

grafana-ansible-collection/roles/grafana/templates/grafana.ini.j2

Lines 116 to 127 in 2e7fd05

	# Alerting
	[alerting]
	{% if grafana_alerting != {} %}
	enabled = true
	{% for k,v in grafana_alerting.items() %}
	{% if k != 'enabled' %}
	{{ k }} = {{ v }}
	{% endif %}
	{% endfor %}
	{% else %}
	enabled = false
	{% endif %}

It is suggested as below.

Confirm that you don’t intend to upgrade your legacy alerts by disabling legacy alerting (optionally enable Grafana Alerting) in your configuration file.

BTW, keep it is the same as README,

grafana-ansible-collection/roles/grafana/README.md

Line 53 in 2e7fd05

| `grafana_alerting` | {} | [alerting](http://docs.grafana.org/installation/configuration/#alerting) configuration section |

Reference:

https://grafana.com/docs/grafana/v10.4/alerting/set-up/migrating-alerts/#what-happens-if-i-dont-upgrade-from-legacy-alerting-to-grafana-alerting-before-installing-grafana-11

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[ishanjainn]

cc @voidquark Is this related to your PR?

[voidquark]

cc @voidquark Is this related to your PR?

Yes, my PR fix also this.