Feature to deactivate the beacon on leader's demand

[nb9960]

Similar to issue #4 in this case too, beacon location should be pre-specified; otherwise, it might lead to process failure. Notification scheduler feature of flutter_local_notifications can also be used to inform users (leader as well as followers if any) when Hike has started.
As of now, startsAt field in beacon model is specified as DateTime.now while creating an hike, createHike dialog needs to be modified to pre-schedule the beacon.

[devansh12b2]

I will like to work on this issue please assign it to me @nb9960 .

[devansh12b2]

For deactivating beacon: No such mutation exists in the backend.