Support Ephemeral / Temp Mode

[srilman]

One useful use-case for Denali is as an ephemeral catalog for testing purposes. So a temporary database and warehouse. Right now, we can kind of replicate it with the following flags / environment variables:

DENALI_API_PORT=5000 DENALI_WAREHOUSE_PATH=/tmp/iceberg DENALI_DATABASE_URL=":memory:" DENALI_DATABASE_TYPE="sqlite3" denali start

It would be convenient if instead there was a flag that did this automatically, something like (or maybe --ephemeral:

denali start --temp

Some additional nice features to include:

• Randomly choose port, retrying if port is occupied
• Randomly generated local warehouse path, cleanup on exit