feat: Fully support Events API v2 in PagerDuty step

[kiyanmair]

What

• Implement full support for PagerDuty's Events API v2.
• Enable triggering incidents using the Events API.
• Add a new event value to the PAGERDUTY_ALERT_TYPE enum.
• Add a new PAGERDUTY_SEVERITY argument.
• Update the step specification.
• Update the step documentation.
• Bump the step's minor version.
• Maintain backwards compatibility.
• Resolve PagerDuty step does not fully support Events v2 API #696.

Why

• PagerDuty's Events API was only supported for creating change events.
• Triggering incidents was only possible with PagerDuty's REST API.
• More details in the linked issue.

Notes

• I have not tested this PR.
• I'm a new contributor to this repo and might have missed something.
• This PR only supports the trigger event action, not acknowledge or resolve, because they add complexity to the step and I'm not sure they're useful in the Codefresh context.

[kiyanmair]

@dustinvanbuskirk @lrochette Hey folks! 👋 Any chance you can take a look at this PR?

[lrochette]

I alerted our Dev team