Add support for "Active VPC peering connections per VPC" quota.

[kevincox]

Summary

Add support for "Active VPC peering connections per VPC" quota.

This is modelled after the "Subnets per VPC" quota which needs very similar logic however it is slightly more complicated since we need to consider peering connections where we the requester, accepter or both.

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This work is owned by my employer Yugabyte, however I have permission to release code under the AGPL v3 license as stated below.

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[kevincox]

TODO: I'm not sure how to get the "active" region. Removing this check would result in VPCs being reported for multiple regions.

[kjkuan]

I believe it should be self.conn._client_config.region_name ?