FIX(promql-to-scrape, promql-to-dd-go): Proxy configuration from environment variables

[ztalarick]

Changed client.go files to make API calls respect Proxy configuration from environment variables.

What was changed

Changed http client to initialize with environment variable proxies.

Why?

When using the sample server it wouldn't send API calls through our corporate proxy and API calls to temporal cloud would fail.

How was this tested:

Tested by monitoring logs and observed working /metrics endpoint.

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[taonic]

@ztalarick Thanks for the PR. I can help you to merge once the CLA is signed.