Alert manager should support SNMP as receiver type

1. Proposed title of this feature request
   - Integration of Alertmanager and  SNMP traps

2. What is the nature and description of the request?
   - Alertmanager should support SNMP as a receiver type
   - Red Hat doesn't support an SNMP integration out-of-the-box; the only solution to configure it in such a way is to use [2] and following [3] to modify the Alertmanager configuration secret and create a webhook integration to the SNMP notifier.

3. Why does the customer need this? (List the business requirements here)
   - No configurations are getting involved with SNMP integrations supported and recommended by Red Hat. The customer needs external tools to be able to send SNMP traps from the Alert Manager of OpenShift, and it would be directly integrated.

4. List any affected packages or components.
   - Alertmanager

Resources:
[1] Is it possible to configure SNMP trap on CoreOS nodes part of RHOCP4 cluster?
https://access.redhat.com/solutions/6217051 

[2] Alertmanager configuration
https://github.com/maxwo/snmp_notifier#alertmanager-configuration 

[3] Applying a custom Alertmanager configuration
https://docs.openshift.com/container-platform/4.13/monitoring/managing-alerts.html#applying-custom-alertmanager-configuration_managing-alerts