refs AE-124
When running pre-deploy migrations that add a new column, if an application server loads the schema on a shard where the migration has already run, and tries to run queries on a shard where the migration has not already run, it can lead to errors. Fix this by allowing ignored_columns to append to its value dynamically through Consul.
Change-Id: I3b13e0fd2ac066e1439d3d314d71f2ebd8938e0c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/310561
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jacob Burroughs <jburroughs@instructure.com>
QA-Review: Aaron Ogata <aogata@instructure.com>
Product-Review: Aaron Ogata <aogata@instructure.com>
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