Expand notification targets

[effigies]

Is your feature request related to a problem? Please describe. Third-party consumers of OpenNeuro datasets, such as BrainLife or NEMAR, may want to subscribe to push notifications for new datasets or snapshots. We currently have the ability for users to subscribe to emails through the web UI.

Describe the solution you'd like An API interface to subscribe to events through (potentially) non-email notification methods, such as a POST. This will presumably need to be a whitelisted set of targets for now.

Describe alternatives you've considered Suggest subscribing to GitHub RSS feeds?

[effigies]

Along these lines, it could be a nice feature to allow any search query to produce an RSS feed so people can easily subscribe to it.