Adding Custom Headers to Requests in Prometheus AnalysisProvider

[ucpr]

What would you like to be added:

I would like to include specific headers containing secrets when making requests using the Prometheus Analysis Provider as a Provider for ADA.

Why is this needed:

When using New Relic as a Prometheus Analysis Provider, it is necessary to send a request with a secret in the header

• https://docs.newrelic.com/docs/query-your-data/grafana-integrations/set-configure/configure-new-relic-prometheus-data-source-grafana/
• https://pipecd.dev/docs-v0.48.x/user-guide/managing-piped/configuration-reference/#analysisproviderprometheusconfig