Fix NullPointerException when parsing X-Preview-Date HTTP header

Fixed a bug in the Headless Server's media delivery endpoint where a NullPointerException caused erroneous error responses for preview requests. The X-Preview-Date header value was incorrectly passed to Long.getLong(), which looks up a JVM system property by name rather than parsing a numeric string. The header is now correctly parsed as an RFC 1123 HTTP date using DateTimeFormatter.RFC_1123_DATE_TIME. Malformed date values are gracefully handled with a warning log, and the current date is used as a fallback.

(CMS-31035)

Headless: Prevent image transforamtion for non transformable objects

Headless media delivery had a problem delivering non transformable SVG images. This bug was fixed,

(CMS-30823)