Bugfix: Use sized initializers for the media sender cfg and callbacks

[ghbogarin]

Description:

The plugin compiled against the latest MOQ5 version was failing to publish video/audio due to mis-fired callbacks. Latest version of MOQ5 need sized initializers in order to work. As per docs of moq_media_sender_callbacks_init:

/* Pointer-only initializer: clears and stamps ONLY the frozen v0 prefix
 * (through on_subscriber_left). It cannot know the caller's storage size, so
 * it never touches the appended on_ready/on_closed/on_track_closed fields --
 * they stay disabled (struct_size == the v0 prefix). To SET any appended
 * callback, initialize with moq_media_sender_callbacks_init_sized(cb,
 * sizeof *cb) instead. */
MOQ_API void moq_media_sender_callbacks_init(moq_media_sender_callbacks_t *cb);

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This change is