feat: Added a not eq operator to predicates

[sandeshbhusal]

"$.data[?(@.id != 2.2)].id"
"$.data[?(@.title != "check")].id"

Also, while running the integration tests, I ran into a couple of issues (from https://github.com/Orange-OpenSource/hurl/blob/master/CONTRIBUTING.md):

$ cd integration
$ python3 server.py >server.log 2>&1 &

There is no server.py file in integration/. It's instead inside integration/hurl.

$ python3 ssl/server.py >server-ssl.log 2>&1 &

There is also no ssl/ folder in this repo.

I think these could be a separate doc PR.

Looking forward to reviews on this PR! :)