Fix Android Background Notification taps not opening app.

[andymoyle]

I'd been frustrated at not being able to get a tap on a notification in the background opening the app.
Turns out changing AndroidManifest.xml

<activity android:excludeFromRecents="true" android:exported="true" android:name="org.apache.cordova.firebase.OnNotificationReceiverActivity" android:noHistory="true" android:taskAffinity="" android:theme="@android:style/Theme.Translucent.NoTitleBar"/>
to

<activity android:excludeFromRecents="true" android:exported="true" android:name="org.apache.cordova.firebase.OnNotificationReceiverActivity" android:noHistory="true" android:taskAffinity="" android:theme="@android:style/Theme.Translucent.NoTitleBar">
            <intent-filter>
                <action android:name="MYCLICKACTIVITY" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

Works a treat.
BUT - the json sending to firebase needs to include

'click_action':'MYCLICKACTIVITY'

in the Android>notification section

No idea how to make a change/pull request.
Might someone smarter than me test its' replicable and do the honours please.