Running a build at a runtime with a RocksDB database fails

When the nextjs plugin runs a build, nextjs spawns a new process to do the SSG build, and that process can try to access the database which fails because RocksDB does not support multi-process access. The error is:
```
Error: IO error: While lock file: /user.../hdb/database/system/LOCK: Resource temporarily unavailable opening database
```
We can look into trying to run nextjs builds in worker thread (reproduce the command line execution). Or the alternate resolution to that is probably to implement https://github.com/HarperFast/rocksdb-js/issues/490 and then implement support for falling back to read-only mode in Harper, so that nextjs can do the build.