Add introductory sentence for 'verder' command

[wbaccinelli]

When the 'verder' command is received, a sentence clarifying that a dialog will be resumed should used:
Oké. Het dialoog waar je mee bezig was zal hierna weer verder gaan of, in sommige gevallen, weer starten vanaf het begin

See PerfectFit-project/testing-tickets#48 (comment)

If this is merged into the intervention after 1/10/2023, contact Milon with the merging time so she can keep track.

[nelealbers]

Such a sentence already exists in case of the weekly reflection and goal-setting dialogs, which are the two dialogs that can be resumed also in the middle.