Add new feature to delete list of attributes by ID

Request a PyMISP method that accepts a list of attributes to be deleted. In version 2.4.133 api.py exposes method delete_attribute(id) which works fine. If run on the MISP server host the rate is about 22 per second, which is tolerable. Still it seems silly to POST 100,000 or other horribly large number of times when I could POST once. FWIW, we would like to use this feature to clean the mess of soft-deleted attributes left by the delta-merge algorithm on fixed-event feeds.

I'm hoping this is trivial bcos apparently the MISP server supports this already according to this comment thread; it requires an event ID (altho the delete_attribute method does not), but that doesn't seem hugely onerous:

https://github.com/MISP/MISP/issues/6010#issuecomment-660891990

What's the right way - extend the delete_attribute method to accept a list or add a new method? If you will please reply with the team's preference then I will make a proposal for a change to api.py. Thanks for listening.

Start in api.py with the existing delete_attribute(id) method, then read the referenced MISP issue 6010 comment about the server-side batch deletion API and its event ID requirement. Decide whether the client should extend that method or add a new one, and consider the work done when PyMISP exposes the server-supported batch deletion operation without requiring one POST per attribute.