Kyma Bindings Based on Token Requests - Create Endpoint

[ralikio]

Description

The following PR introduces generation of kubeconfig for Kyma Bindings (#284) in /v2/service_instances/{instance_id}/service_bindings/{binding_id} endpoint. Generated kubeconfig is returned under the credentials field in the API response. The kubeconfig is generated based on K8S TokenRequests.

Changes proposed in this pull request:

• binding creation PUT endpoint implementation in bind_create.go,
• BindingTokenExpirationSeconds config to set up token expiration time,
• extended kubeconfig provider to provide a clientset client for k8s,
• e2e test that checks cluster access by using generated kubeconfig.

[kyma-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[github-actions]

Add one of following labels

- kind/feature -> Use it when you want to submit a new feature

- kind/enhancement -> Use it when you modify or improve an existing feature

- kind/bug -> Use it when you fix a bug

[MarekMichali]

/lgtm