Improve and fix problems for running DevFile API tests

[musienko-maxim]

What does this PR do?

Fix and improve problems which were described in the https://issues.redhat.com/browse/CRW-5023 issue

During this work, I found the following problems:
* When we generate files from https://api.github.com/repos/eclipse-che/che-devfile-registry/contents/devfiles  We can often face rate limits for unauthorized requests. To increase limits, we can add a GitHub token with an auth header 
* When we use the Inbuld devfile registry on OpenShift and Kubernetes platform - the objects to devfiles URLs are different and we need to manage it.
* There is no way to set k8s custom namespace/OpenShift projects for running APIDevfiles tests

Screenshot/screencast of this PR

What issues does this PR fix or reference?

https://issues.redhat.com/browse/CRW-5023

How to test this PR?

• If we use generating files using https://api.github.com/repos/eclipse-che/che-devfile-registry/contents/devfiles/ URL just set up envs., and run /che/tests/e2e/configs/sh-scripts/runDevfileAcceptanceTests.sh
• If we use the registry from a cluster the example of environments for running:

MOCHA_DIRECTORY=api;
NODE_TLS_REJECT_UNAUTHORIZED=0;
TEST_NAMESPACE=admin-che;
TS_API_TEST_KUBERNETES_COMMAND_LINE_TOOL=kubectl;
TS_PLATFORM=kubernetes;
TS_SELENIUM_BASE_URL=https://192.168.49.2.nip.io/;
USERSTORY=DevfileAcceptanceTestAPI

PR Checklist

As the author of this Pull Request, I made sure that:

• The Eclipse Contributor Agreement is valid
• Code produced is complete
• Code builds without errors
• Tests are covering the bugfix or new feature
• The repository devfile is up to date and works
• Sections What issues does this PR fix or reference and How to test this PR completed
• Relevant user documentation updated
• Relevant contributing documentation updated
• CI/CD changes implemented, documented and communicated

Reviewers

Reviewers, please comment how you tested the PR when approving it.

[dmytro-ndp]

looks good to merge