slack: potential upgrades

[ddkohler]

• incorporate information about the queue
• add ability to see more details of acquisition (perhaps a command to get start.json, or add a file attachment in reply. We don't want to overcrowd the feed.) If gridscan plan, we should extract the axes.
• merge wt5 and slack services (to save on resources)
• consider using block kit to format feed messages
• fetch: send a resaved data file to reduce filesize.
• for simpler installation, programmatically create the app and the channel