Check for data folder on startup

Currently, when starting up for the first time (running standalone, outside
of Docker), bitwarden_rs panics when the `openssl` tool isn't able to create
`data/rsa_key.pem` due to the `data` dir not existing. Instead, print a more
helpful error message telling the user to create the directory.

src/util.rs

@@ -358,6 +358,15 @@ pub fn format_naive_datetime_local(dt: &NaiveDateTime, fmt: &str) -> String {
     format_datetime_local(&Local.from_utc_datetime(dt), fmt)
 }
 
+//
+// Deployment environment methods
+//
+
+/// Returns true if the program is running in Docker or Podman.
+pub fn is_running_in_docker() -> bool {
+    Path::new("/.dockerenv").exists() || Path::new("/run/.containerenv").exists()
+}
+
 //
 // Deserialization methods
 //