Add native EteSync support

[4jNsY6fCVqZv]

EteSync "Secure, end-to-end encrypted, and privacy respecting sync for your contacts, calendars and tasks." Reference to the discussion in the Planner repository alainm23/planify#307 (comment)

I have no experience with EteSync myself, but I find the idea of end-to-end encryption of sensitive data in the context of elementary OS very useful.
This issue should provide room for discussion. Consciously also about possible alternatives, how the desired qualities can be provided independently of certain products.

[danirabbit]

Closing as "Out of Scope" because Tasks uses Evolution Data Server to abstract backends. An EteSync backend would need to be written for EDS.

[danirabbit]

it looks like there's a Summer of Code proposal to add EteSync in EDS already: https://wiki.gnome.org/Outreach/SummerOfCode/2020/Ideas

[4jNsY6fCVqZv]

That was my information on which I based this issue :)
Should currently already work without the module. Although not as elegant as with an official EDS integration. See this comment: alainm23/planify#307 (comment)

So how do you and others feel about my idea?

[tasn]

@danrabbit, EteSync is now in EDS! \o/ Should this be reopened? I guess it's related to elementary/switchboard-plug-onlineaccounts#133?