in_calyptia_fleet: add support for net.* properties for the upstream connection [backport #10998 to 4.0]

[pwhelan]

Summary

Add support for net.* properties for in_calyptia_fleet, ie: net.dns.mode to TCP for some networks or setting the net.dns.resolver to use the legacy DNS resolver.

Description

This PR hooks up the support for net* properties for the upstream connection the in_calyptia_fleet plugin uses. Among the main reasons for this is for the support for setting the dns resolver.

This requires a change to the custom_calyptia plugin as well. With this PR it is now possible to configure the network settings like so:

[CUSTOM]
    Name calyptia
    Fleet_Name test-fleet
    net.dns.resolver legacy
    net.connect_timeout 60
    API_KEY ********

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Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change
• Debug log output from testing the change
• Attached Valgrind output that shows no leaks or memory corruption was found

Backporting

• Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch pwhelan-fleet-set-upstream-net-properties-4.0

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