fix: enable configuring state_dir with runtime configuration

[kate-goldenring]

Instead of fixing the state_dir, we can set the local_app_dir which is a fallback if the state_dir is not set in runtime config like so:

state_dir = "/Path/to/state-dir/

Walk through

I confirmed this fix works with the following steps using a simple TODO app that creates a SQLite DB in the state store:

$ git clone [email protected]:rylev/spin-todo.git
$ cd spin-todo
# create a directory for the state store
$ mkdir foo
# configure the state dir in runtime config -- note, app root is at `/` so no volume mount needed
$ echo state_dir=\"/.configured" > runtime-config.toml
$ spin build
$ spin registry push ttl.sh/spin-sqlite-todo-123:48h 
$ spin kube scaffold --from ttl.sh/spin-sqlite-todo-123:48h --replicas 1 --runtime-config-file _scratch/runtime-config.toml | k apply -f -
# get container id
$ sudo crictl ps
# now use it to get process id (PID)
$ crictl inspect <container-id> | grep pid
12345
# ensure the SQLite DB is under the configured state dir
$ ls /proc/12345/root/.configured
sqlite_db.db

If runtime config is not set -- uses default state_dir of .spin at /

$ sudo ls /proc/12345/root/.spin
sqlite_db.db

[Mossaka]

LGTM!