contentTitle property
Call notification content title and full screen incoming call activity header
If contentTitle on CallKeepBaseConfig is set up, it would default to be ContentTitle(callerName)
or contentTitle(appName) if callerName is null
If you override contentTitle it would superseed the CallKeepBaseConfig.contentTitle
You can assign it to empty String to have notification content title be callerName,
and full screen header will be "Call from CallKeep", which you can override in your
android/app/src/main/res/values/strings.xml
with key call_header
Implementation
final String contentTitle;