getAttachment retrieves a specific attachment by its message and attachment
IDs.
automations/get-outlook-attachment.automation.ts
messageId and attachmentId are required opaque Graph IDs. Optional account
selects the Microsoft binding.
Returns attachmentId, name, type, size, inline state, optional content
metadata, and file: File when Graph returns base64 file bytes. Item and
reference attachments generally do not produce a File.