Inconsistent Tails' Persistent Storage feature use

[torinthiel]

Describe the change

Document relevant set of Tails' persistent storage features

How will this impact SecureDrop users?

Clearer documentation.

Additional context

The page for initial creating of USB drives mentions enabling persistent storage and enabling all features later.
This is however inconsistent with the image just below, which has network connections feature disabled.

While it might make sense to persist network connections (and maybe even Tor Bridge settings) for Admin Workstation, it has little sense to do so for SVS which is set up with no network connectivity.

Furthermore, as of Tails 5.19 (I haven't checked previous versions) there's 'Electrum Bitcoin Wallet' feature that has little sense in either context. Pidgin settings seem to also have little relevance and might even encourage using it from Admin Workstation which probably should be avoided. Possibly same goes for Thunderbird - the OSSEC emails should go to an account that's visible not from Admin Workstation.