[feature request] add ability to configure projects/prefixes in yaml file

I have ~250 different GCP projects, with different needs. In some projects I just only need to scrape Composer metrics, in the other projects I need to scrape only BigQuery metrics, or only Compute metrics. Sometimes I need to scrape i.e. Composer+Bigquery, or Compute+Loadbalancing metrics.

I don't want to scrape all the metrics just to catch few metrics that I need in a particular projects. This is cost inefficient (pay per request) and results in throttling by GCP (by the way caused by uncontrollable parallelism).

My workaround is to run simultaneously many exporters with different command line parameters - but it's difficult to maintain.

Is it possible to add ability to configure stackdriver_exporter using .yml file? i.e.

project1-prod: 
  - composer.googleapis.com
project2-prod:
  - composer.googleapis.com
  - bigquery.googleapis.com
project3-prod:
  - bigquery.googleapis.com
  - compute.googleapis.com

The issue names no files, tests, or entry points. Begin by locating the exporter’s project and metric-prefix configuration paths, then determine how a YAML mapping could select metrics per GCP project. Done means projects can specify different metric prefixes without running multiple exporter instances, while avoiding unnecessary metric requests.