Conversation RenameReservedPathsMigration migration helper

https://gitlab.com/gitlab-org/gitlab-ce/tree/master/lib/gitlab/database/rename_reserved_paths_migration/v1

This class or group of classes is used by multiple database migrations to rename Git repositories. We need to make sure this goes via Gitaly.

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Stages:

• RPC Design: Create Issue

• ~"Client Implementation": Create Issue

• Server Implementation: Create Issue

• ~"Acceptance Testing": Create Issue

RPC Endpoints:

• Endpoint::Name

Known Client Routes:

• Known client endpoints

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