Add missing security headers

[yathomasi]

Similar to https://github.com/iterative/iterative.ai/pull/704 for cml.dev.

https://securityheaders.com/?q=https%3A%2F%2Fcml-dev-security-header-yaovt6.herokuapp.com%2F&followRedirects=on

[github-actions[bot]]

9855d6a

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