Clashing DuckDB database access

[EJOOSTEROP]

In at least the following scenarios the DuckDB database file cannot be read:

1. When an ELT pipeline is running, Superset cannot access the database at the same time and all the graphs on the dashboard fail. Workaround: wait for the ELT pipeline to complete.
2. When a Superset dashboard contains multiple graphs, at most one will be shown when looking at the dashboard. The others have error messages. Workaround: manually refresh each graph in the Superset UI.
3. When multiple ELT pipelines run at the same time, some will fail. Workaround: re-run the failed jobs.

This is understood to be at least a partially fixable issue (have Superset open the database file with read-only privileges). Though I don't know how at the moment.

There is unlikely to be a DuckDB fix to avoid ELT clashes (as ELT needs write access to the database file).