support fully v2 event api

[NargiT]

[Edited for a global concern]

Support fully v2 api and allow to override all fields.

missing fields: timestamp,client, client_url, links, images

Usage:
  pdagent enqueue [flags]

Flags:
      --class string           The class/type of the event
      --component string       Component of the source machine that is responsible for the event
  -y, --dedup-key string       Deduplication key for correlating triggers and resolves
  -t, --event-action string    The type of event
  -f, --field stringToString   Add given KEY=VALUE pair to the event details (default [])
  -g, --group string           Logical grouping of components of a service
  -h, --help                   help for enqueue
  -k, --routing-key string     Service Events API Key
  -e, --severity string        The perceived severity of the status the event is describing with respect to the affected system (default "error")
  -u, --source string          The unique location of the affected system
  -d, --summary string         A brief text summary of the event

v2 event api https://developer.pagerduty.com/api-reference/b3A6Mjc0ODI2Nw-send-an-event-to-pager-duty