Suggest encryption of stored --authentication-header-overrides values

[rjackson-fr]

Describe the solution you'd like

When storing --authentication-header-overrides on a connection, the values should be encrypted in connections.json, not included on stdout when running the frodo command, and value excluded or masked when using --curlize param

[vscheuber]

@rjackson-fr I missed this one in 3.1.0. Will fix it in the next release.