Add all `c.BinderHub.*` properties used in chart to Values.yaml

[manics]

Follow-up to https://github.com/jupyterhub/binderhub/pull/1597

Adds all c.BinderHub.* properties used in chart to Values.yaml for visibility, except for buildDockerConfig which will be dealt with separately.

$ git grep Values\\.config\\. -- helm-chart/

helm-chart/binderhub/templates/_helpers.tpl:{{- if .Values.config.BinderHub.buildDockerConfig }}
helm-chart/binderhub/templates/_helpers.tpl:{{- $dockerConfig := merge $dockerConfig .Values.config.BinderHub.buildDockerConfig }}
helm-chart/binderhub/templates/container-builder/daemonset.yaml:      nodeSelector: {{ .Values.config.BinderHub.build_node_selector | default dict | toJson }}
helm-chart/binderhub/templates/deployment.yaml:      {{- if .Values.config.BinderHub.use_registry }}
helm-chart/binderhub/templates/deployment.yaml:          {{- if .Values.config.BinderHub.use_registry }}
helm-chart/binderhub/templates/deployment.yaml:        {{- if .Values.config.BinderHub.auth_enabled }}
helm-chart/binderhub/templates/deployment.yaml:          value: {{ (print (.Values.config.BinderHub.hub_url_local | default .Values.config.BinderHub.hub_url | trimSuffix "/") "/hub/api/") }}
helm-chart/binderhub/templates/deployment.yaml:            path: {{ .Values.config.BinderHub.base_url | default "/" }}versions
helm-chart/binderhub/templates/deployment.yaml:            path: {{ .Values.config.BinderHub.base_url | default "/" }}versions
helm-chart/binderhub/templates/image-cleaner.yaml:      nodeSelector: {{ .Values.config.BinderHub.build_node_selector | toJson }}
helm-chart/binderhub/templates/secret.yaml:{{- if or .Values.config.BinderHub.use_registry .Values.config.BinderHub.buildDockerConfig }}

This helps reduce the "hidden" configuration in the Helm Chart.