extract linkedin into a gem and add tests

fixes: CNVS-12119

test plan:
regression test linkedin functionality

Change-Id: I9cec121d641db37d4c8f6a04966e766e9f8b293e
Reviewed-on: https://gerrit.instructure.com/33473
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Jason Madsen <jmadsen@instructure.com>