[Bug] IotDB pods crash with OOM because we calculate the memory based on the node not pod resources

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/iotdb/issues) and found nothing similar.

### Version

latest

### Describe the bug and provide the minimal reproduce step

Start IOTDB datanode and confignode pods with memory limits, for example 8 GB, and allocate 8 GB of resources to each pod.

Pods keep crashing with OOM errors because the JVM is trying to allocate 16 GB of memory.

### What did you expect to see?

```
# When running in a container/pod, use cgroup memory limit instead of host memory
if [ -f /sys/fs/cgroup/memory.max ]; then
# cgroup v2
cgroup_mem=`cat /sys/fs/cgroup/memory.max`
if [ "$cgroup_mem" != "max" ]; then
cgroup_mem_in_mb=`expr $cgroup_mem / 1024 / 1024`
if [ "$cgroup_mem_in_mb" -lt "$system_memory_in_mb" ]; then
system_memory_in_mb=$cgroup_mem_in_mb
fi
fi
elif [ -f /sys/fs/cgroup/memory/memory.limit_in_bytes ]; then
# cgroup v1
cgroup_mem=`cat /sys/fs/cgroup/memory/memory.limit_in_bytes`
cgroup_mem_in_mb=`expr $cgroup_mem / 1024 / 1024`
if [ "$cgroup_mem_in_mb" -lt "$system_memory_in_mb" ]; then
system_memory_in_mb=$cgroup_mem_in_mb
fi
fi
```
8GB

I would expect the memory to be auto-calculated based on the pod resources (8 GB), not the node resources (32 GB).
```
# scripts\conf\datanode-env.sh
system_memory_in_mb=`free -m | sed -n '2p' | awk '{print \$2}'` returns 32 GB.
```

### What did you see instead?

32 GB and a lot of pod restarts

### Anything else?

```
# iotdb\WORKING_CONFIGS.md

## 2) JVM Memory (Linux)

Edit these files:
- conf/confignode-env.sh
- conf/datanode-env.sh

Set MEMORY_SIZE explicitly to avoid auto-sizing surprises.

### ConfigNode memory

```bash
# conf/confignode-env.sh
MEMORY_SIZE=2G
```

### DataNode memory

```bash
# conf/datanode-env.sh
MEMORY_SIZE=8G
``````

Why are there no env varibales for this setting?
Do you expect the clouad env to manualy go and change this limit?

This is a hack, and we should not have to do this in a pod
```
- IOTDB_JMX_OPTS=-Xmx4G
```

### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!

Start with conf/confignode-env.sh and conf/datanode-env.sh, especially the system_memory_in_mb calculation using free -m. Compare the cgroup v2 and v1 memory-limit cases described in the issue, then verify that a pod limited to 8 GB sizes the JVM from that limit rather than the host's memory and avoids OOM restarts.

Written by the indexing model from the issue text.