Support configuration management API

[Hayk Davtyan]

Is your feature request related to a problem? Please describe.
Add a new API that will allow configuring and updating the main Prometheus configuration file (prometheus.yml) through the API.

Describe the solution you'd like
This API should be based on the following API.

Describe alternatives you've considered
N/A

Additional context
In addition to all of this, the feature should be visible on the UI as well where users can easily add or update Prometheus targets, etc.