Replace target with restate-data as the default storage directory

[tillrohrmann]

This fixes #1276.

[AhmedSoliman]

What do you think about using the PlainNodeID as a sub-directory name under restate-data (e.g. restate-data/N0) to make it trivial to run multiple nodes on the same host?

[tillrohrmann]

What do you think about using the PlainNodeID as a sub-directory name under restate-data (e.g. restate-data/N0) to make it trivial to run multiple nodes on the same host?

I think this makes a lot of sense. So instead of configuring the individual directories for different components separately, we would allow specifying something like a working directory (e.g. restate-data) where we create a subdirectory for the node (restate-data/N0) and then the different restate components could create subdirectories in the node-scoped working directory (restate-data/N0/db, restate-data/N0/logs, etc.).

This change requires a bit more work than what I did in this PR. Would you be ok, @AhmedSoliman, if I tackled it as a follow-up since it is not strictly required for the single node Restate setup?

[AhmedSoliman]

@tillrohrmann absolutely, go for it.

[tillrohrmann]

Merging this PR now.