User Mapping - FE - Fix banner copy

What does this MR do and why?

Update copy of accept banner

And use link for group.

(Implements part of #480719 (closed))

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. In rails console enable the flag

    Feature.enable(:importer_user_mapping)

2. In your local db, find the user you're logged in as (eg. id number 1) in the import_source_users table and take note of that id

3. Change the status cell to 1. See the state machine in app/models/import/source_user.rb for the various statuses.

4. You may also need to modify the columns reassign_to_user_id and reassigned_by_user_id to the id of your logged in user

5. If the placeholder_user_id column is NULL, you may also need to add a valid placeholder id

6. Save db changes

7. Navigate to /import/source_users/[current_user_id]

8. Click the approve button

Related to #480719 (closed)