Improve OSSF Scorecard Token-Permissions check by tightening GitHub Actions permissions

[gaganhr94]

{
      "name": "Token-Permissions",
      "score": 0,
      "reason": "detected GitHub workflow tokens with excessive permissions",
      "details": [
        "Warn: jobLevel 'actions' permission set to 'write': .github/workflows/pr-gh-workflow-approve.yaml:19",
        "Warn: no topLevel permission defined: .github/workflows/kind-e2e.yaml:1",
        "Warn: no topLevel permission defined: .github/workflows/knative-go-build.yaml:1",
        "Warn: no topLevel permission defined: .github/workflows/knative-go-test.yaml:1",
        "Warn: no topLevel permission defined: .github/workflows/knative-security.yaml:1",
        "Warn: no topLevel permission defined: .github/workflows/knative-stale.yaml:1",
        "Warn: no topLevel permission defined: .github/workflows/knative-style.yaml:1",
        "Warn: no topLevel permission defined: .github/workflows/knative-verify.yaml:1",
        "Info: found token with 'none' permissions: .github/workflows/pr-gh-workflow-approve.yaml:1"
      ],
}

Several top level permissions are missing, as a result of which the score is zero for this particular check of the OpenSSF scorecard. This score can go to 10 if all the top level permissions are set to content: read (i.e, minimal permissions at the top level)

More details on this check:
https://github.com/ossf/scorecard/blob/main/docs/checks.md#token-permissions