Migration to version 9

[max3903]

Todo

https://github.com/OCA/maintainer-tools/wiki/Migration-to-version-9.0

Modules to migrate

• knowledge by @naousse in [9.0] knowledge #75
• document_page by @naousse in [9.0] document_page #76
• document_page_approval by @naousse in [9.0] document_page_approval #77
• attachment_preview
• attachments_to_filesystem
• document_choose_directory
• document_no_unique_filenames
• document_reindex
• document_url