Added unit test for getting SatelliteAccessConfigJsonFile

SatelliteConfig introduced getSatelliteAccessConfigJsonFile method to
support getting satellite_access_config.json file in config update flow.
SatelliteConfigParser leverages the same to get the content of
satellite_access_config.json file. Added a unit test for the same.

Test: atest SatelliteConfigParserTest
Bug: 391782433
Flag: com.android.internal.telephony.flags.carrier_roaming_nb_iot_ntn
Change-Id: I61551573bcd0bc29cb43a0882d1f9b290eb91148