BluetoothMetrics: Upload GATT server and client connection state change events

* clientConnect(): GATT client starts connecting to a GATT server.

* onConnected(): GATT client completes connection successfully or fails.

* clientDisconnect(): GATT client starts disconnecting from a GATT server.

* onDisconnected(): GATT client completes disconnection from a GATT server. (Always successfully)

* onClientConnected(): GATT server successfully receives a connection or disconnection from a GATT client (depending on the value of boolean “connected”)

Bug: 233400948
Test: BluetoothInstrumentationTests
Tag: #feature
Change-Id: If0fc3f489c0abffb1bf7d2ef87a6c554d45ebbbf