Filter queries using correct operators

[Atmire-Kristof]

References

• Fixes Discovery facets displaying incorrect items #915
• Fixes Search component does not allow you to use FacetValue with authority operator #368

Description

This PR ensures operators are added when sending requests containing facets or filters through discovery. The operators are retrieved from the relevant part of the search link returned by the server, rather than have the UI construct the query on its own.

Instructions for Reviewers

Changes made:

• A util file was added called search.utils.ts containing a method (getFacetValueForType()) to retrieve the relevant facet value with operator from the search link returned by the server. The util file also contains functions to strip an operator from a filter's value or add one to it.
• When a user types or selects a suggested filter, the operator "query" is added to the value
• Modified labels to strip the operator (using the util function) wherever the filter values displayed (below the search box for example)

How to test:

• Visit the discovery page
• Add filters by selecting one from the sidebar or typing them yourself (and/or selecting from the suggestion dropdown)
• Verify the requests sent contain the correct operators for each filter value
• Verify any values displayed in the UI don't contain the operators

Known Issue
Issue #3057 on the REST API might cause unexpected behaviour.

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[lgtm-com]

This pull request introduces 2 alerts when merging cb6381f into 8d44b5d - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class

[tdonohue]

👍 Thanks @Atmire-Kristof . This code looks good & works well.

@artlowel mentioned in today's meeting we may want to eventually think about updating the backend to use templated links (as originally described in this comment). However, this current implementation seems "good enough" for now, and it fixes the immediate bugs.