"Unknown field" error on Prometheus Operator

Issue

• When some fields like follow_redirectsare used under http_config in the secret alertmanager-main, the following error shows up in Prometheus Operator pod:

prometheus-operator fails to parse this configuration due to an unknown field (follow_redirects):
level=error ts=2022-01-14T08:10:38.69780826Z caller=klog.go:116 component=k8s_client_runtime func=ErrorDepth msg="Sync \"openshift-monitoring/main\" failed: provision alertmanager configuration: base config from Secret could not be parsed: yaml: unmarshal errors:\n  line 4: field follow_redirects not found in type alertmanager.httpClientConfig\n  line 116: field follow_redirects not found in type alertmanager.httpClientConfig"