Add function that will return setting length

[eva-cerncic]

Context

It would be very useful to have function:
size_t user_setting_get_length_with_id(uint32_t id)
and
size_t user_setting_get_length_with_key(uint32_t id)

or similar.

For now I can implement generated function that will return size from id, but it would be very useful to have this in the module. @TjazVracko

[eva-cerncic]

As discussed, not needed as get functions provide same functionality.