Cubestore on K8s panics w/o setting CUBESTORE_PORT

**Describe the bug**
A clear and concise description of what the bug is.

Cubestore panics if deployed on K8s without explicitly setting `CUBESTORE_PORT` to `3306`.
Please note that a service must also be deployed to surface the error (which is weird).

**To Reproduce**
Steps to reproduce the behavior:
1. Start a minikube cluster (or any cluster/playground e.g. [katacoda](https://www.katacoda.com/courses/kubernetes/creating-kubernetes-yaml-definitions)
2. Create a service

```yaml
apiVersion: v1
kind: Service
metadata:
name: cubestore
labels:
app: cubestore
spec:
ports:
- port: 3030
targetPort: 3030
selector:
app: cubestore
```

3. Deploy the service `kubectl apply -f service.yaml`
4. Create a deployment

```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: cubestore
spec:
replicas: 1
selector:
matchLabels:
app: cubestore
template:
metadata:
labels:
app: cubestore
spec:
containers:
- name: cubestore
image: cubejs/cubestore:v0.28.8
ports:
- containerPort: 3030
```
5. Deploy `kubectl apply -f deployment.yaml`
6. If you get the pod's logs you will see the error:

```
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ParseIntError { kind: InvalidDigit }', cubestore/src/config/mod.rs:458:55
stack backtrace:
0: rust_begin_unwind
at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399/library/std/src/panicking.rs:493:5
1: core::panicking::panic_fmt
at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399/library/core/src/panicking.rs:92:14
2: core::option::expect_none_failed
at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399/library/core/src/option.rs:1300:5
3: cubestore::config::Config::default
4: cubestored::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
```

If we add the environmental variable it works 🤯 :

```diff
apiVersion: apps/v1
kind: Deployment
metadata:
name: cubestore
spec:
replicas: 1
selector:
matchLabels:
app: cubestore
template:
metadata:
labels:
app: cubestore
spec:
containers:
- name: cubestore
image: cubejs/cubestore:v0.28.8
ports:
- containerPort: 3030
+ env:
+ - name: CUBESTORE_PORT
+ value: "3306"
```

**Expected behavior**
A clear and concise description of what you expected to happen.

Since the [CUBESTORE_PORT defaults to 3306](https://cube.dev/docs/reference/environment-variables#cube-store) I would expect to not have to specify it as an env var.

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Version:**
[e.g. 0.4.5]

Cubestore v0.28.8

**Additional context**
Add any other context about the problem here.