Add user category filter in user resources

[samtang-coconut]

Description

This PR adds user category filter to the user resource.

Motivation and context

We want to be able to filter users within a user category when booking an appointment after service and meeting method are selected.

How has this been tested?

Added the following tests to reflect usage of filtering by user category in the user resource:

• will set a user category filter using a string
• will set a user category filter using a number

Types of changes

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

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