5.0: Use RelationListIterator

[adriendupuis]

Question	Answer
JIRA Ticket	N/A
Versions	5.0
Edition	All

To get all relations, use RelationListIteratorAdapter + BatchIterator instead of ContentService::countRelations() + ContentService::loadRelationList()

Follows #2544 and in particular this comment.

Previews:

• Content management > Content API > Browsing content > Viewing content metadata > Relations
  • https://doc.ibexa.co/en/5.0/content_management/content_api/browsing_content/#relations
  • https://ez-systems-developer-documentation--2548.com.readthedocs.build/en/2548/content_management/content_api/browsing_content/#relations
• Templating > Embed and list content > Embed content > Embed Relations with a custom controller
  • https://doc.ibexa.co/en/5.0/templating/embed_and_list_content/embed_content/#embed-relations-with-a-custom-controller
  • https://ez-systems-developer-documentation--2548.com.readthedocs.build/en/2548/templating/embed_and_list_content/embed_content/#embed-relations-with-a-custom-controller

Checklist

• [ ] Text renders correctly
• [ ] Text has been checked with vale
• [ ] Description metadata is up to date
• [ ] Redirects cover removed/moved pages
• [ ] Code samples are working
• [ ] PHP code samples have been fixed with PHP CS fixer
• [ ] Added link to this PR in relevant JIRA ticket or code PR

[github-actions[bot]]

Preview of modified files

Preview of modified Markdown:

• docs/content_management/content_api/browsing_content.md
• docs/templating/embed_and_list_content/embed_content.md