Add support for the Pre-request handler script

[mateuszjanczak]

Hi, could you please add support for the Pre-request handler script that was added in IntelliJ 2022.3 Beta?

In the testing section, it would be very useful to be able to use environment variables in assertions.

More context: https://youtrack.jetbrains.com/issue/IDEA-239365/client.global.get-returns-null-for-variables-defined-in-http-client.env.json#focus=Comments-27-6556849.0-0