Support Sync contexts

**Is your feature request related to a problem? Please describe.**

Given two valid contexts, it would be nice to have the ability to synchronize a particular entity ie. dashboards between two contexts.

Source context could use grafana instance or the storage system as an input while the destination should always be a grafana insurance.

**Describe the solution you'd like**
A clear and concise description of what you want to happen.

Example : `gdg sync dashboards staging production `
`gdg sync datasources --backup staging production`