When searching for users, also include integration_id in the list of fields that are searched

[ColinMurtaugh]

This idea has been developed and deployed to Canvas

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Currently when you search for a Canvas user via the Accounts > People page or via the REST API, the system tries to match the query against the name, email, user_id, login_id and sis_id fields. We would like to also be able to find users who have an integration_id that matches the search query. 

The ability to search for users based on sis_id is based on the read_sis/manage_sis permissions. Since the visibility of the integration_id is governed by the read_sis permission elsewhere in Canvas, it seems reasonable to also use the read_sis/manage_sis permission to determine whether or not the integration_id is searchable. 

This seems like it would require a fairly small change to user_search.rb.

The use-case for this idea has to do with integrating Canvas with a third-party service; it needs to be able to look up Canvas users by their integration ID.