Add OpenVSX detector

[Kiblyn11]

Description:

Add a detector for OpenVSX tokens used by OpenVSX registry: https://open-vsx.org/ It use an available API endpoint on a legitimate namespace and look for permission issue error which means the token exist and is valid.

Checklist:

• [x] Tests passing (make test-community)?
• [x] Lint passing (make lint this requires golangci-lint)?

[CLAassistant]

All committers have signed the CLA.

[shahzadhaider1]

@Kiblyn11 Thanks for your contribution! I’ve done an initial review; great work so far. I’ve left some feedback for minor improvements. I’ll do a thorough review once the updates are in.

[Kiblyn11]

@shahzadhaider1 Thanks for your initial review. I have to admit I hacked this at first to check some assumptions without looking at contributing guides. I updated the detector type to be specific.