out_pgsql: dynamic load library on windows

[costinmrr]

This is in response to the changes requested in https://github.com/fluent/fluent-bit/pull/3811. If we're on the right path with these changes, I will edit the documentation and go on to meet the requirements so the PR can be accepted.

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[Worek]

Hi. When this support will be merged? We wanted to use it in our app but unfortunately its running on windows. Also could you mention this issue in your docs? I spent half of day looking why pqsql is not working.

[hongaar]

@fujimotos this PR addresses the issues you raised in #3811. Curious to hear your opinion on these changes and also whether there's anything we can do to get this merged. Thanks!

[sxd]

@costinmrr can you fix the DCO issue and also squash your commits so we can review only one package?