Support disabling built-in feedback feature via config

[amcclain]

We have an admittedly very bare-bones built-in dialog to collect feedback.

We do not see this getting much use at all, so in many apps it might be considered noise or the team would prefer to get feedback some other way. But the real concern is an app that doesn't have email support configured - there a user might submit feedback but someone would need to actively look in the Admin > User Activity > Feedback tab to find it.

We should support a config to centrally disable the service, hiding the menu option on the client, hiding the admin tab, and throwing were the endpoint to be called in some other way. Could be xhFeedbackConfig, which would also let us spec a dedicated email for feedback, should it be enabled.

Note that there is an appMenuButton prop available to hide the built-in menu option, but this config would allow it to be toggled w/o requiring a code change.