fix datasource json and secure json fields

[pb82]

Fixes #38

The problem was that grafana uses a type of map[string]interface{} for the jsonData and secureJsonData fields of a data source. The operator-sdk does not support code generation for interface{} fields. Instead of only allowing strings we're now providing structs for the most common jsonData and secureJsonData options as documented here.

Verification steps:

1. Install the operator using the quay.io/integreatly/grafana-operator:fix-extra-json tag.
2. Create the example data source.
3. The operator will restart grafana.
4. After a few seconds, log in to Grafana and check the data sources.
5. The Prometheus data source should exist and the tlsSkipVerify option should be checked.