Sync values file and template. Add error handling

[5nafu]

This PR syncs the values.yaml to the variables used inside the templates by adding missing defaults and moving tolerations, ... back to top level as described in #27.

Additionally added a jsonschema file for validation of supplied values.

The error message would look like this (example from helm lint with an "old-style" values.yaml)

==> Linting chart
[ERROR] values.yaml: - daemonset: Additional property tolerations is not allowed

[ERROR] templates/: values don't meet the specifications of the schema(s) in the following chart(s):
docker-hub-rate-limit-exporter:
- daemonset: Additional property tolerations is not allowed


Error: 1 chart(s) linted, 1 chart(s) failed

According to helm/helm#12842 custom error messages are not yet possible.

Notes:

• I did not add very detailed properties for complex objects like securityContext in order to keep maintainability.
• I commented out service.nodePort, hostNetwork and hostPID as these variables do not have a default value and the linter would have flagged them when left empty.
• The schema file was generated by losisin/helm-values-schema-json