Validate HTTP connectivity for Agent traces port

[nikita-tkachenko-datadog]

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What does this PR do?

Improves connectivity check for Agent traces port.

Current check only verifies that a TCP socket can be opened using the Agent's host and configured traces port.
Traces are sent over HTTP, so it is possible that there is TCP connectivity, but not HTTP connectivity (for example, if there is an HTTP proxy in between Jenkins and the Agent).

The improved check verifies HTTP connectivity: it sends an HTTP request to the agent's /info endpoint. The check is considered successful if the info can be retrieved.

Description of the Change

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