Add a complete document resource to the n8n node with 21 operations
covering documents, versions, and signatures — matching the MCP
specification. Also add the sendSigningNotifications tool to the MCP
API for triggering pending signature reminders.
n8n operations: create, get, getAll, update, delete, archive,
unarchive, getVersion, getAllVersions, createDraftVersion,
updateVersion, deleteDraftVersion, publishMajorVersion,
publishMinorVersion, requestApproval, voidApproval, getSignature,
getAllSignatures, requestSignature, cancelSignature,
sendSigningNotifications.
Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>