Test: Add Net Promoter Score feedback support

[joaomoreno]

• @weinand
• @seanmcbreen (review the spec)

This shouldn't be tested but rather code reviewed. The behaviour we are trying to achieve is described in #9686.

[weinand]

Tested through debugging:

• Found an incorrect check that would prevent the dialog from ever showing.
• The notification does not show because of Cannot use message service before workbench is up #9769

[Tyriar]

Closing this off since the test is complete.