New/Edit Assign users page: Allow a user to assign a user(s) to an EBSCO KB

As a FOLIO System Admin that manages multiple EBSCO KBs in one tenant
I must assign a user to one EBSCO KB credentials
So that the user gets to access to the eholdings s/he manage

General Requirements

• If a library has only one EBSCO KB credentials configured then it is not required for them to assign users.
• This requirement only applies to a tenant that has configured multiple EBSCO KB credentials
• The user can only be assigned to one set of EBSCO KB credentials.
• If multiple EBSCO KBs have been configured and a user has not been assigned to a set of EBSCO KB credentials then s/he will not get access to the eHoldings app regardless of assigned eholdings permissions

UI requirements

• Create a new page: Assigned users
• Default page: https://drive.google.com/file/d/16Z4_2cQDSZoYyDCAPw6GnE9g1Tgi1ZCS/view?usp=sharing
• Click Assign users should open the Find Users plug-in
  
• Display assigned users
  
• Display order of the Assigned users list should be Alphabetical (A-Z) order by Last name
• Unassign a user from knowledge base confirmation modal
  
• If a user is added to a second set of EBSCO KB credentials then display a modal error message that indicates the Users that already have been assigned to credentials.
  Screenshot
  

Acceptance Criteria

Given I click on Assign users button
When I select a user
Then display the user on the list of assigned users

Given I have assigned a user to Knowledge base - Smith
When I remove a user(s)
Then display the Unassign a user from a knowledge base confirmation modal message

Given I have assigned a user to a set of EBSCO KB credentials
When s/he has already been assigned to a set of EBSCO KB credentials
Then display the Already have been assigned to another knowledge base modal message

Given I have assigned a user OR unassigned a user
When the backend endpoint is not returning a response
Then display an toast notification error message Unable to complete this operation. Please try again