OK, I finally found what I needed to do. I needed to add a dashboard providers section in my values.yaml file, like so:
dashboardProviders:
dashboardproviders.yaml:
apiVersion: 1
providers:
- name: default
orgId: 1
folder: ""
type: file
disableDeletion: false
editable: false
options:
path: /var/lib/grafana/dashboards/default