feat: try to load proxy from environment if not provided via input

[derdanne]

Issue #, if available:

1061

Description of changes:

The current proxy implementation does not load the proxy configuration from the runner environment as stated in the documentation.

This PR solves this by trying to load the proxy configuration from the runner environment, when no "http-proxy" input is given. The used node package checks for the specific endpoint url of the given STS regional endpoint and also respects no_proxy configurations.

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