Temp http server for "export" feature - Making it downloadable.

[MichelDiz]

This is kind of a poll to see if it's an interesting feature. If you have something to add on it. Be Welcome.

If you would like help sending us a PR it would also be interesting.

The idea is to create a temporary path to download the gzip generated by export and/or accessible by IP on whitelist. And possibly request a password to do the download.

My 2 cents:
I see that this feature would be interesting for creating automated actions. Like the HARD upgrade. And I think it could be extended to a kind of "Dgraph's internal webhooks" to help with other possible automations.

[manishrjain]

We could accept a path for where the export should be done as part of the HTTP request.