Update pd2pg to support Pagerduty API v2.

[caquino]

This PR updates pd2pg to support Pagerduty API v2.

• Removal of /api/v1 URIs
• Removal of PAGEDUTY_SUBDOMAIN as v2 API uses api.pagerduty.com

This was tested importing about 3 million records (incidents and log_entries mostly) without any issues.

I would appreciate more tests thou.

Thanks

[zenramri]

Nice work @caquino.
Works as expected

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