Context

This MR upgrades QCheck tests to QCheck2 for lib_proxy_server_config

Warning

~~This MR conflicts with !5459 (merged). Whichever is merged last will have to be rebased and corrected.~~

Edit: !5459 (merged) has been merged, this MR has been rebased and adapted.

Related: #1583

n/a Document the interface of any function added or modified (see the coding guidelines)
n/a Document any change to the user interface, including configuration parameters (see node configuration)
n/a Provide automatic testing (see the testing guide).
n/a For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
Select suitable reviewers using the Reviewers field below.
Select as Assignee the next person who should take action on that MR

Edited Jun 08, 2022 by nbacquey