Add request count / duration metrics for external data providers

[mark-adams]

Describe the solution you'd like
We're currently building an in-house External Data provider. However, there's currently an observability gap where it is difficult to understand the impact that External Data provider latency has on the overall performance of the validation webhook.

To solve this, I'd love to see the addition of the following metrics:

Name: gatekeeper_external_data_provider_request_count
Description: The number of requests made to an external data provider
Tags: external_data_status: [success, system_error], external_data_provider_name: [(provider name attribute)]
Aggregation: Count

Name: gatekeeper_external_data_provider_request_duration_seconds
Description: The external data provider response time in seconds
Tags: external_data_status: [success, system_error], external_data_provider_name: [(provider name attribute)]
Aggregation: Distribution

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.