fix(integration-test): fixing test to use apps/v1 for deployment

[mynktl]

Why is this PR required? What issue does it fix?:

What this PR does?:

• This PR fixes test code to use apps/v1 for the deployment.
• remove example/00-prereqs.yaml
• update Kubernetes version to v1.20.1 in github workflow

Does this PR require any upgrade changes?:

If the changes in this PR are manually verified, list down the scenarios covered and commands you used for testing with logs:

Any additional information for your reviewer?: Mention if this PR is part of any design or a continuation of previous PRs

Checklist:

• [ ] Fixes #
• [x] PR Title follows the convention of <type>(<scope>): <subject>
• [ ] Has the change log section been updated?
• [ ] Commit has unit tests
• [ ] Commit has integration tests
• [ ] (Optional) Are upgrade changes included in this PR? If not, mention the issue/PR to track:
• [ ] (Optional) If documentation changes are required, which issue on https://github.com/openebs/openebs-docs is used to track them: