This pull request migrates testdata to coreplugin streaming capabilities,
this is mostly a working concept of streaming plugins at the moment,
the work will continue in the following pull requests.
Refactor to allow shared contract between core and external backend plugins
allowing core backend data sources in Grafana to be implemented in same
way as an external backend plugin.
Use v0.67.0 of sdk.
Add tests for verifying plugin is restarted when process is killed.
Enable strict linting for backendplugin packages
