SNOW-1333163: Add support for default proxy configuration

[vc-74]

Description

Although the current code supports HTTP proxies, it does not allow to use the default proxy configuration.

This PR allows using the default proxy by specifying the useProxy=true parameter in the connection string without specifying an explicit proxy (proxyHost, proxyPort...).

Checklist

• Code compiles correctly
• Code is formatted according to Coding Conventions
• Created tests which fail without the change (if possible)
• All tests passing (dotnet test) (I only executed HttpUtilTest to avoid having to configure a connection to Snowflake)
• Extended the README / documentation, if necessary
• Provide JIRA issue id (if possible) or GitHub issue id in PR name

[github-actions]

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[vc-74]

I have read the CLA Document and I hereby sign the CLA

[vc-74]

recheck

[sfc-gh-knozderko]

Hello @vc-74. Please add here a comment with text: "I have read the CLA Document and I hereby sign the CLA".

I also created a new PR, because I needed to update it and add some new logic: #997

Please review the new PR and add also a comment in it: "I have read the CLA Document and I hereby sign the CLA".