Update valid choices docs for PagerDuty integration

[mlcooper]

Documentation Page

https://docs.datadoghq.com/dora_metrics/setup/failures/?tab=pagerduty

Issue Description

Account is no longer a valid choice when setting up a new webhook in PagerDuty. It is now Service or Team for valid choices:

[kayayarai]

Hi Mitchell, apologies for the delay in responding. Looking at PagerDuty's webhook API docs, it looks like Account is still a thing at least in some situations https://developer.pagerduty.com/docs/webhooks-overview#filter. Perhaps it shows up only in some contexts.

We're working on an update to the docs to put more emphasis on Team and Service types because they are at least more likely to be useful than Account.

Thank you so much for raising this.