net: lwm2m: Timeseries data cache read update

Added support for handle case when all data is not possible to
add in 1 message for Send and Observed Notification.

Notification continuous pending timeseries data is triggred
by iMIN attribute.

Send Operation generate continuous message in multiple lwm2m
message.

Normal Read by server only report back latest stored data.

Signed-off-by: Juha Heiskanen <juha.heiskanen@nordicsemi.no>