csis: Read complete service before notifing it is Connected

With this patch, we make sure all the characteristic are read, before
CONNECTED signal is sent to the Java layer

Bug: 279990836
Test: atest BluetoothInstrumentationTests
Test: atest bluetooth_csis_test
Tag: #feature
Change-Id: I8f8a1f6a2896c518fc9b3c4090849a2e5379911f