Add new data policy fields

[timcowlishaw]

• enable_forwarding allows forwarding to be enabled or disabled per device

• precise_location allows users to choose whether precise (5dp) or approxmite (3dp + 2dp of noise) locations are stored.

On deploying we will need to run migrations, then run rake devices:truncate_and_fuzz_locations in order to truncate the existing locations to 5dp.

[timcowlishaw]

Addresses #307

[timcowlishaw]

We're not convinced that 3dp + noise is quite as "imprecise" as we were hoping: will possibly send a follow up PR to make imprecise locations a little noisier

[sentry-io[bot]]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ ActionView::Template::Error: undefined method `data_policy' for #<Device id: 16254, owner_id: 7346, name: "CitzenFACE", descri... V0::MeController#index View Issue
• ‼️ NameError: undefined local variable or method `enable_forwarding' for #<Device id: 17545, owner_id: 6556, na... app/models/device.rb in forward_readings? View Issue
• ‼️ NameError: undefined local variable or method `enable_forwarding' for #<Device id: 13104, owner_id: 7659, na... app/models/device.rb in forward_readings? View Issue
• ‼️ NoMethodError: undefined method `precise_location' for #<Device id: nil, owner_id: 6556, name: "TGH_MAIN_NURSEWS... V0::DevicesController#create View Issue

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[timcowlishaw]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

* ‼️ **ActionView::Template::Error: undefined method `data_policy' for #<Device id: 16254, owner_id: 7346, name: "CitzenFACE", descri...** `V0::MeController#index` [View Issue](https://iaac.sentry.io/issues/5544588186/?referrer=github-pr-bot)

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(This was just momentary due to the migrations not being run yet)