Add regions and endpoints for the Pinpoint `mobiletargeting` service

[marramgrass]

Endpoints and regions as listed at https://docs.aws.amazon.com/general/latest/gr/pinpoint.html.

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Before opening a PR, please make sure you have:

• Run mix format using a recent version of Elixir
• Run mix dialyzer to make sure the typing is correct
• Run mix test to ensure no tests have broken (also please make sure you've added tests for your particular change, where appropriate).

[bernardd]

Thanks @marramgrass!