Use target endpoints for Service Catalog list and item

[gosiexon-zen]

Description

Removed mock and call to Custom Objects API and instead use target endpoints created for Service Catalog:

/api/v2/help_center/service_catalog/items.json
/api/v2/help_center/service_catalog/items/{id}.json

For EAP we are reading the service item id from the URL as we are passing it by clicking the item on the list and redirecting. to the service item page. For GA we will read it from curlybars.
Added component for description for service item to handle showing the "read more" button when the description is shorter.
Jira issue GG-3951

Screenshots

Checklist

• 📗 all commit messages follow the conventional commits standard
• ⬅️ changes are compatible with RTL direction
• ♿ Changes to the UI are tested for accessibility and compliant with WCAG 2.1.
• 📝 changes are tested in Chrome, Firefox, Safari and Edge
• 📱 changes are responsive and tested in mobile
• 👍 PR is approved by @zendesk/vikings