Added option for android background location sync

[BWMuller]

This should resolve the following issues: https://github.com/Almoullim/background_location/issues/206, https://github.com/Almoullim/background_location/issues/204, https://github.com/Almoullim/background_location/issues/202, https://github.com/Almoullim/background_location/issues/131, https://github.com/Almoullim/background_location/issues/8

This add background location when the app is closed, screen locked or similar as well as start on boot (this requires headless update handler). It also adds more option to the notification such as action and custom channel_id.

Note that one of the changes this does bring in is that when for android someone chooses background location the /method callback for location doesn't trigger anymore due to the headless callback existing. This means that all location updates for android come via the headless handler and for ios come via the getLocationUpdates as they normally do.

Naturally when background location is not enabled then it won't be an issue.

[MoralCode]

@BWMuller thanks for keeping this up to date and sorry for not checking in on this! Was there a particular method you used to test this? I'd love to have some independently verifiable way to know that it works since I cant really directly test it.

[BWMuller]

@MoralCode Unfortunately I haven't been able to get around granting permissions as of yet for creating a standalone test that can just be run on ios/android so that you have an independent method of verification

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