Limit ticket message body size to 1MB

Starting from Jan 31, 2023, ticket message body_text and body_html size is going to be limited to 1MB.

• Endpoints such as create or update message will return HTTP error response (status code 400) when the size of body_html or body_text attributes exceeds 1MB.
• Ticket messages created before the change will be truncated to fit the 1MB limit.

Note that the limit does not affect message attachments.