That would need to be mqtt-persistence.cfg
But I do not think it does what you think it does; this has nothing to do with graphing, nothing to do with reading data from sensors.
mqtt-persistence is to allow openHAB to publish (never read) Item data to an MQTT broker.
I gotta say that one of the most annoying thing about helping people on this forum is needing to pry out of the those asking for help even the most basic information necessary to provide that help.
If I ask a question, I require the answer to that question before I can proceed. Read my reply again. There are two questions there.
The * does not mean what you think it means, perhaps.
You have asked to persist all members of a group called home_temp.
You maybe meant to persist the Item home_temp, or some group that Item is a member of?
Your Item home_temp is not a Group type, so you do not want home_temp* in your rrd4j.persist file, because that is a group request.
If you want to store an item in rrd4j, just say so in the .persist file home_temp : strategy = everyChange
After you have got this simple version working, you might want to come back to change it.
If you have several Items to store - home_temp, home_humi, outside_temp, outside_humi etc. etc.
Put each of those Items in a group in your Item definitions
Group persist_Group "group for rrd4j persisting"
Number home_temp "temperature smt [%.1f °C]" <temperature> (persist_Group) { channel=...
Number home_humi "humidity smt [%.1f %%]" <humidity> (persist_Group) { channel=...
Now you alter your rrd4j.persist file persist_Group* : strategy = everyChange
and this will store every member of the group. This is the special meaning of the * here.