Upgrade mb-solr to 9.4.0

The SOLR_HOME has changed to /var/solr/data in latest versions, the actual
data lives at /var/solr/data/data and the cores should go under SOLR_HOME.
The plugins should go in SOLR_INSTALL_DIR/lib.

Dockerfile

@@ -1,6 +1,6 @@
 ARG MAVEN_TAG=3.9.6-eclipse-temurin-17
 ARG SOLR_NAME=solr
-ARG SOLR_TAG=9.4.0
+ARG SOLR_TAG=9.4.0-slim
 
 FROM maven:${MAVEN_TAG} AS builder
 
@@ -36,17 +36,14 @@ RUN apt-get update && \
         && \
     rm -rf /var/lib/apt/lists/*
 
-COPY --from=builder \
+COPY --from=builder --chown=solr:solr \
      mb-solr/target/mb-solr-0.0.1-SNAPSHOT-jar-with-dependencies.jar \
-     /opt/solr/server/solr/lib/
+     /opt/solr/lib/
 
-ENV SOLR_HOME /opt/solr/server/solr
-COPY ./mbsssss $SOLR_HOME/mycores/mbsssss
-
-# Creating directory for seach indexes data
-# and fix permissions
-RUN mkdir $SOLR_HOME/data && \
-    chown -R solr:solr /opt/solr /opt/solr-$SOLR_TAG
+COPY --chown=solr:solr ./mbsssss /var/solr/data/mycores/mbsssss
+# Create directory and set permissions to SOLR user here so that they are propagated to the mounted volume
+RUN mkdir /var/solr/data/data && \
+    chown -R solr:solr /var/solr/data/data
 
 ARG MAVEN_TAG
 ARG SOLR_NAME