Fix GraphQL API for clearing issue contacts

What does this MR do and why?

Fix GraphQL API for clearing issue contacts

The API was handling: adding, removing and setting a new list, but not setting an empty list (e.g. clearing/removing all).

Changelog: fixed

Screenshots or screen recordings

Before:

After:

How to set up and validate locally

1. Create an issue in the project
2. Enable CRM
3. Create a test contact
4. Add a new contact to the issue
5. Run the below GraphQL query https://gdk.test:3000/-/graphql-explorer

   mutation {
     issueSetCrmContacts(input: {
       projectPath: "flightjs/mood-test"
       iid: "1"
       contactIds: []
       operationMode: REPLACE
     }) {
       errors
       issue {
         customerRelationsContacts {
           nodes {
             firstName
           }
         }
       }
     }
   }

MR acceptance checklist

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Related to #427038 (closed)