- Add mtd_meta_clear to allow specific analytics-meta to handle their clear
operation specific to their type.
- Clear mtd's attached when analytic-meta is freed. When the buffer where
analytics-meta is attached is not from a buffer pool
gst_analytics_relation_meta_clear will not be called unless we explicitly call
it in _free. This important otherwise _mtd_clear are not called and lead to
leak if embedded mtd's allocated memory
- Un-ref in transform if it's a copy
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6026>
