Increase the limit of linked items that can be added at the time

What does this MR do and why?

Increase the limit of linked items that can be added at the time from 3 to 10

Screenshots or screen recordings

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Before	After

How to set up and validate locally

Prerequisites:

1. Enable the OKRs feature as mentioned in the OKRs docs (e.g. ::Feature.enabled?(:okrs_mvc, Project.find(<PROJECT_ID>)) and the namespace must have Ultimate plan).
2. Enable the feature flag Feature.enable(:linked_work_items)

Steps to verify:

1. Login with any user
2. Go to any Project > Issues > List
3. Create an new Objective under New issue split button
4. Go to Objective detail page
5. Under 'Linked Items', click on Add button to open the form
6. Select any relationship
7. Search/Select 10 or more work items and check the message

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #416558 (closed)