Settings: Convert notifications to use NotificationChannel (1/2)

Test Setup:
===========
HW DUT: Pixel O
Remote: MecApp (SAP Client)

Usecase:
1) Connect from MecApp.
2) Accept SAP connection on DUT.

Expected Behaviour:
Notification popup for SAP connected should be displayed on UI
which provide option for user to disconnect SAP connection.

Observed Behaviour:
Notification popup for SAP connected is not displayed on UI so user
is not able to initiate disconnection from SAP server.

Root cause:
In Android O, notifications are hidden by default.
This must be changed to use notification channels so that the
priority of the notifications can be updated.

Fix:
Add notification channel before building notification from SAP.

Test: Checked if now notification for SAP connect can be seen in
notification bar when SAP is connected allowing user to disconnect.

Bug: 38331825
Change-Id: I67b0a3fd7f1df857c6288150edbef80d4a953490
(cherry picked from commit c5c434b205948c7bf6bea50fc55521904c896ce6)