Very big Landing Pages can exceed 65,535 bytes in generated JSON, which will throw SQL exception on saving/publishing.

Steps to reproduce
1. Clean installation of eZ Platform 2.5 EE
2. Log in as admin to the back office.
3. Edit "Home" Landing Page in Page Builder
4. Add code block containing:
https://pastebin.com/WEa8FWAr (JIRA allows 32,767 characters, so please follow this link for example text)
5. Publish page.

Result

An exception occurred while executing 'INSERT INTO `ezpage_attributes` (name, value) ...  

SQLSTATE[22001]: String data, right truncated: 1406 Data too long for column 'value' at row 1

Expected Result
Landing Page publishes normally.