Add Sandbox package option to dev script

General MR

Summary

Adds an optional -s flag to the dev/renovate-dev.sh script that changes the package import targets from the current graduated Big Bang packages to the Sandbox packages instead.

This came up while working on implementing the renovate.json config for a new package currently in Sandbox (Mimir) that we wanted to test before it graduates to Big Bang/Universe/Product.

Relevant logs/screenshots

N/A

Linked Issue

big-bang/apps/sandbox/mimir#18

Upgrade Notices

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