Fix snapshot location in Dockerfile

[jonastheis]

Description of change

After changing to WORKDIR /tmp in the Dockerfile, the default location for the snapshot ./snapshot points to an invalid location. Therefore, changing the location to /tmp/snapshot.bin should fix the problem and make it usable without specifying the path to the snapshot when starting the container.

[karimodm]

But why was the workdir changed to /tmp ? This might break other things depending on how volumes are configured on the compose files.

Database locations for the resulting image are not copied over from the build enrvironment:

+# Fix permission issue when mounting volumes.
+COPY --chown=nonroot:nonroot --from=build /tmp/ /tmp/mainnetdb/
+COPY --chown=nonroot:nonroot --from=build /tmp/ /tmp/peerdb/
+
+WORKDIR /tmp
+USER nonroot
+

I think this is done simply to have those directories available and owned by nonroot when starting goshimmer.
I don't think it was necessary to do it this way, but at this point I think your change is the simplest to patch the issue.