[Observability] add .slo-observability.* index privileges to built in editor and viewer roles

[dominiqueclarke]

Today, the editor and viewer roles do not contain the appropriate index privileges for SLO users.

This PR updates the index privileges to include the .slo-observability.* indices.

Note

I'm not an Elasticsearch dev. I have not ran or tested this or know much about how to operate in Java project. I'd welcome feedback on how to test and collaboration with an Elasticsearch dev to get this over the finish line.