Input failed to start after https

@jan,

I tried that configuration only because I had the same error for the below config which my original config is based on

  - GRAYLOG_HTTP_EXTERNAL_URI=https://graylog.sysnetgs.com:9000/
  - GRAYLOG_HTTP_PUBLISH_URI=https://graylog.sysnetgs.com:9000/
  - GRAYLOG_HTTP_ENABLE_TLS=true
  - GRAYLOG_HTTP_TLS_CERT_FILE=/certs/graylog.crt
  - GRAYLOG_HTTP_TLS_KEY_FILE=/certs/graylog.key

let me know if there is anything worng in the above