Robust automatic retry on choppy network conditions

Clone of https://github.com/vector-im/element-android/issues/3837

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Related to https://github.com/vector-im/element-android/issues/2803

Couldn't automatic retry be a thing for when all delivery failures are only network-related?

Telegram and WhatsApp have the ability to send messages whenever you want, after which a clock icon will appear that'll wait until it is either delivered or sent.

With Element I often get the feeling that delivery failures are *also* given in turbulent network conditions, which make retrying extremely cumbersome.

I'd really like to have such a robust delivery system such as Telegram and WhatsApp be in place in Element, where firing off a message on a good server (though a bad network), will have its delivery time not be an if, but a when. (Whenever the network allows it, keep retrying until it does.)

Start by reading the linked Element Android issues 3837 and 2803 to understand the related discussion; this issue names no iOS files, tests, or entry points. The work would need a defined scope for retrying network-only delivery failures, with completion measured by reliable eventual delivery when connectivity returns.

Written by the indexing model from the issue text.