Add post API

[avlitman]

Adding new API:
/api/v1/alerting/rules | POST

Jira-tickets:
https://issues.redhat.com/browse/CNV-71552

tested on CRC cluster:

create user alert:

curl -s -H 'Content-Type: application/json' -X POST http://localhost:9001/api/v1/alerting/rules -d '{"alertingRule":{"alert":"crcDemo4","expr":"vector(1)","for":"0m","labels":{"severity":"warning"},"annotations":{"summary":"crc demo"}},"prometheusRule":{"prometheusRuleName":"user-pr","prometheusRuleNamespace":"default","groupName":"custom-group"}}' | jq .
{
  "id": "crcDemo4;8efcb1d24fd9570c1f8b47811b00802247808a0dfa852a1802ae40b0d38eddb7"
}