Add support for gardener provider in clusterloader2

[KesavanKing]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR adds support of Gardener Provider in clusterloader2 framework.

Special notes for your reviewer:

Gardener already takes care of Conformance test coverage - testgrid view. This PR really helps to execute Performance tests for Gardener.

Gardener has its own managed Prometheus. So the prometheus client is created by consuming configurations from Provider Config.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: KesavanKing
Once this PR has been reviewed and has the lgtm label, please assign wojtek-t for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• clusterloader2/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

Hi @KesavanKing. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.