feat: [CO-1258] FileUploadServlet allow uploading huge attachments

[keshavbhatt]

Allow user upload huge attachments using service/upload endpoint.

What has changed:

• The lbfums parameter in the upload request now makes the FileUploadServlet use the zimbraFileUploadMaxSizePerFile account attribute to enforce the maximum upload file size limit.
• ParseMimeMessage (while saving attachments from MimeMessage using FileUploadServlet) now handles smartlink attachments separately, applying limits enforced by zimbraFileUploadMaxSizePerFile instead of zimbraMtaMaxMessageSize.
• The SaveDraft, GetMsg, and SearchResponse APIs now return the size of the MimeMessage that accounts for smartlinks, allowing the Mail composer to determine if attachments should be converted to smartlinks. Additionally, the encodeMessageAsMP method in ToXML now prevents adding empty MimeMessage elements to responses, reducing the need for client-side checks.
• Added tests and made some minor refactoring.