Validate against GCP Databricks

[ivanvyd]

Same situation as #51, for GCP. docs/compatibility.md records GCP Databricks as not tested;
everything has only run against Azure.

What closing this looks like

export DATABRICKS_HOST="https://<your-workspace>.gcp.databricks.com"
export DATABRICKS_TOKEN="<token>"
export LAKESPEAK_LIVE_AGENT="<your agent name>"
dotnet test -c Release --filter "Category=Live"

Then add a row to the Clouds table in docs/compatibility.md and the README's verification
table, with the date and what was run — including anything that failed.

The live suite costs warehouse time and writes nothing.