Store the Alertmanager notification configurations as a service configuration

[Ebaneck]

Component:

'salt', 'kubernetes', 'alertmanager'

Why this is needed:

For persistence of Alertmanager notification configurations, we need to store these service configurations using a ConfigMap.

Here, we are talking about integrations to Slack, email(smtp), victorops etc

What should be done:

• Define the schema and default values for this ConfigMap
• Deploy the ConfigMap holding these service values
• Template and render the prometheus-operator charts to read cluster and service configurations from the ConfigMaps directly.

Implementation proposal (strongly recommended):

Test plan:

Epic #1996