Enhance Dockerfile and documentation for GeoIP directory permissions

- Updated Dockerfile to create and set ownership for the /var/lib/telemt-gateway directory, ensuring the gateway user has the necessary permissions.
- Added documentation in GEOIP.md to clarify directory permissions required for GeoIP data downloads, including guidance on volume mounting and user ID consistency.

Dockerfile

@@ -12,7 +12,9 @@ RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -ldflags="-s -w" -o /out/gateway
 FROM alpine:3.19
 RUN apk add --no-cache ca-certificates wget \
     && addgroup -S gateway -g 65532 \
-    && adduser -S -u 65532 -G gateway gateway
+    && adduser -S -u 65532 -G gateway gateway \
+    && mkdir -p /var/lib/telemt-gateway \
+    && chown gateway:gateway /var/lib/telemt-gateway
 COPY --from=build /out/gateway /gateway
 USER gateway:gateway
 EXPOSE 8080