Add Sliding Sync `/sync/e2ee` endpoint for To-Device messages #1296

Job	Run time
Calculate list of debian distros	9s
Build wheels on ubuntu-20.04 for x86_64	1m 41s
Build sdist	0s
Build .deb packages (debian:sid)	8m 22s
Attach assets to release	0s
	10m 12s

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