Allow REST file API for single attachment with caption

[mysubcult]

Allow REST file API to handle a single attachment with text/caption instead of sending rendered attachment HTML through the normal text body.\n\nThis keeps file uploads working when the message contains a caption and preserves the existing behavior for plain text and multi-file messages.\n\nRelated Telegram extension PR: LiveHelperChat/telegram#73

[remdex]

Can't accept. You are hardcoding extension which is not the way to go. Implement as separate field in back office where you can define 1+n extensions to be skipped.

[mysubcult]

Updated per feedback. The hardcoded extension list was removed from the REST API action code.\n\nREST API methods now have a back office field, suburl_file_skip_ext, where extensions can be configured as a comma-separated list. The single-file-with-message path reads that field before using �ody_raw_file with {{msg_clean}}.\n\nThe Telegram PR now sets this field to gs, so stickers keep the old skip behavior while other single attachments can be sent through the file API with caption.