fix(server-type): inconsistent base for size units in description

[jooola]

TL;DR

The included_traffic displayed in the server type describe command is using a different base for the size unit from the rest of the sizes.

Expected behavior

Have a consistent base for the size units we display to the users.

Observed behavior

Minimal working example

hcloud server-type describe cpx21

Log output

No response

Additional information

No response

[phm07]

Traffic is actually billed in €/TiB, not in €/TB, so we should adjust that. Then the units would also match.