feat: expose DialContext in Dialer and propagate context

[kruskall]

What does this PR do?

A dialer only exposed the Dial method, making it impossible to correctly propagate context along with timeouts and cancellations.

This PR exposes DialContext in the dialer interface.

The Dial method is kept for backward compatibility.

Why is it important?

We're using NetDialer to create a dialer in apm-server but we are forced to pass the Dial method to the http.Transport because DialContext is not exposed.

This prevents the context from being propagated

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.md

Author's Checklist

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Related issues

[elasticmachine]

💚 Build Succeeded

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History

• 💚 Build #177 succeeded 27ba8ec
• 💚 Build #114 succeeded 774bdf2
• 💔 Build #113 failed b384153
• 💔 Build #111 failed 951a996