HTSP: Expose is_new flag in EPG event data

HTSP: Expose is_new flag in EPG event data

This commit adds the is_new flag to the EPG event data sent to HTSP clients.
By including this property, clients such as Kodi (with the pvr.hts addon)
can now detect whether a broadcast is marked as new and set corresponding
flags (e.g. EPG_TAG_FLAG_IS_NEW in Kodi).

This enhances the metadata available to clients and supports improved EPG
event handling and display.

A corresponding pull request will also be submitted to the pvr.hts project
to make use of this flag when obtaining EPG event guide data from Tvheadend.