Upgrade automatic and manual upgrade screenshots

Originally created by @sajolida on #12365 (Redmine)

Once 3.1 is out:

We should upgrade the automatic upgrade screenshot in /doc/first_steps/upgrade.
We could add another one for manual upgrade so that both contexts are clarified.

But let’s not bother doing that before 3.0 because it would be too painful to be worth it.

Feature Branch: spriver:web/12365-update-upgrader-screenshots

Edited May 15, 2020 by sajolida

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