Added OpenSSF best practices badge to README.md

[Ankitasw]

What type of PR is this?
/area security

What this PR does / why we need it:
This PR adds OpenSSF best practices badge to the repository so that it will be easier to check if we are adhering to security standards and if not, then would be able to raise appropriate issues for the same.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #3062

Special notes to the reviewers:
Please provide feedback on the info provided in OpenSSF related to our project here. I will make desired changes.

Checklist:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

Release note:

Added OpenSSF best practices badge in README.md.

[k8s-ci-robot]

@Ankitasw: This issue is currently awaiting triage.

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[sedefsavas]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sedefsavas

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• OWNERS [sedefsavas]

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