Change directory where apns-conf.xml is stored

When apns are downloaded OTA they are stored directly under data/misc
by system server. Files created there gets assigned with file context
system_data_file which TelephonyProvider cannot read.

In order to make sure that downloaded apns gets a file context TelephonyProvider
can read we create an apns sub directory in init where radio_data_file:s are
created. The data path to where apns-conf is stored is here changed from /data/misc/
to /data/misc/apns/.

This change is aligned with other files that ConfigUpdateInstallReceiver writes.

Test: Trigger Apn update via intent UPDATE_APN_DB
Go to settings/apn-list and verify that newly downloaded are present
Bug: 79948106

Change-Id: I5a9ec262bfbac291cca9fee5accf93eb6c06f253