Don't overwrite security params when editing saved config

WifiConfigController2 sets the security params of a saved config, which
may overwrite @hide fields like SecurityParams#mIsAddedByAutoUpgrade. To
prevent this, only set the security params for a new config, and use the
existing security params for existing configs.

Bug: 262312532
Test: atest WifiConfigController2Test
Change-Id: I9ef5eb8ce2b4208e1fad27bd68fc4f0fad7d1008