Sanitize probe header value written by user before response (#10533)
Sanitize probe header value written by user before response (#10533)

This patch adds `http.EscapeString` to probe header value written by user
before response.

Please also refer to github alert https://github.com/knative/serving/security/code-scanning/4?query=ref%3Arefs%2Fheads%2Fmaster
knative/serving,knative/serving