Add a new Prometheus settings section in operations page

Summary

The overall target is to move all Prometheus related settings from the integrations page to settings page

Goal

In this issue, a new section to handle all prometheus settings within the project operations page is created. The new section will be behind settings_operations_prometheus_service feature flag.

This issue specifically intends to move only the manual configuration part of the Prometheus section to ops page.

Screenshots

New	Old

Technical implementation

Backend

We need to handle update of Prometheus integration inside operations controller.

Frontend

The existing haml page can just be moved over to the settings page.

Acceptance criteria

Changes should be hidden behind feature flag

Endpoint: PUT /*namespace_id/:project_id/-/settings/operations accepts additional parameters:

{
 'prometheus_integration_attributes': {
            'manual_configuration': '0'
            'api_url': 'https://gitlab.prometheus.rocks'
          }
}

Valid parameters are preserved in database and available upon page refresh