add support for transferring data ownership to Bytes via custom deleter

[DenisBiryukov91]

add support for transferring data ownership to Bytes via custom deleter

[YuanYuYuan]

Nit: shall we align with the doc in zenoh-c? https://github.com/eclipse-zenoh/zenoh-c/blob/8974132e1bd49954ebf0a7b6242c8c3f8d21f503/include/zenoh_commons.h#L1480-L1482
In particular, the deleter has a guide for static variables.

[DenisBiryukov91]

Nit: shall we align with the doc in zenoh-c? https://github.com/eclipse-zenoh/zenoh-c/blob/8974132e1bd49954ebf0a7b6242c8c3f8d21f503/include/zenoh_commons.h#L1480-L1482 In particular, the deleter has a guide for static variables.

I added to the docs, that deleter should be a thread safe. There is no need for extra mention for NULL, since Deleter can not be null here and should always a valid callable. It can have an empty implementation if user desires (it is way simpler to provide it in c++ than in c)