Add 5G RAT into Bearer field.

Within APN editor, 5G RAT need to be added into Bearer field.

Bug: 143995814
Test: 1. Build pass.
      2. make RunSettingsRoboTests ROBOTEST_FILTER=ApnEditorTest
      3. check UI:
      3-1. Open APN settings page: Settings > Network & Internet > Mobile Network > Advanced > Access Point Names.
      3-2. Click the 3 dots at the up corner, and then select "New APN" > "Bearer"

Change-Id: If09afd00cf7860c3bbb40be748ca04c9a55ee5b8