Metrics via OpenTelemetry

## Feature Description

Metrics can be exported from Hasura Cloud and Hasura EE to any OpenTelemetry compliant Endpoint.

## User value / outcome

Enterprise users are able to get metrics into their Observability tools, which they can use to monitor the health of their Hasura deployment.

## Current status (design, alpha, beta etc.)

Design

## Resources (e.g. RFCs)

WIP, will be very similar to the [trace exporter](https://hasura.io/docs/latest/enterprise/opentelemetry/) implementation.

Start with the linked OpenTelemetry trace exporter documentation and its implementation, then compare how metrics export would fit Hasura Cloud and Hasura EE. The issue is still at the design/WIP stage, so clarify the supported metrics, endpoint behavior, and acceptance criteria before identifying implementation files. Done means metrics can be exported to a compliant OpenTelemetry endpoint.

Written by the indexing model from the issue text.