**Apache Airflow version**: 2.0.1
**Kubernetes version**: v1.19.7
**Executor**: KubernetesExecutor

**What happened**:

If you have a worker that gets stuck in pending forever, say with a missing volume mount, the task will stay in the queued state forever. Nothing is applying a timeout on it actually being able to start.

**What you expected to happen**:

Eventually the scheduler will notice that the worker hasn't progressed past pending after a given amount of time and will mark it as a failure.

**How to reproduce it**:
```python
from airflow import DAG
from airflow.operators.bash import BashOperator
from airflow.utils.dates import days_ago
from kubernetes.client import models as k8s


default_args = {
    "owner": "airflow",
}

with DAG(
    dag_id="pending",
    default_args=default_args,
    schedule_interval=None,
    start_date=days_ago(2),
) as dag:
    BashOperator(
        task_id="forever_pending",
        bash_command="date; sleep 30; date",
        executor_config={
            "pod_override": k8s.V1Pod(
                spec=k8s.V1PodSpec(
                    containers=[
                        k8s.V1Container(
                            name="base",
                            volume_mounts=[
                                k8s.V1VolumeMount(mount_path="/foo/", name="vol")
                            ],
                        )
                    ],
                    volumes=[
                        k8s.V1Volume(
                            name="vol",
                            persistent_volume_claim=k8s.V1PersistentVolumeClaimVolumeSource(
                                claim_name="missing"
                            ),
                        )
                    ],
                )
            ),
        },
    )
```


**Anything else we need to know**:
Related to:

* #15149 (This is reporting that these pending pods don't get deleted via "Mark Failed")
* #14556 (This handles when these pending pods get deleted and is already fixed)

airflow/kubernetes/kube_config.py
self.worker_container_tag = conf.get(self.kubernetes_section, 'worker_container_tag')
        self.kube_image = f'{self.worker_container_repository}:{self.worker_container_tag}'
        
        
        
        
        self.kube_namespace = conf.get(self.kubernetes_section, 'namespace')
        self.multi_namespace_mode = conf.getboolean(self.kubernetes_section, 'multi_namespace_mode')
        
        
        
        
        self.executor_namespace = conf.get(self.kubernetes_section, 'namespace')
        kube_client_request_args = conf.get(self.kubernetes_section, 'kube_client_request_args')
        if kube_client_request_args:
            self.kube_client_request_args = json.loads(kube_client_request_args)
            if self.kube_client_request_args['_request_timeout'] and isinstance(
                self.kube_client_request_args['_request_timeout'], list
            ):
                self.kube_client_request_args['_request_timeout'] = tuple(
                    self.kube_client_request_args['_request_timeout']
                )
        else:
            self.kube_client_request_args = {}
        delete_option_kwargs = conf.get(self.kubernetes_section, 'delete_option_kwargs')
        if delete_option_kwargs:
            self.delete_option_kwargs = json.loads(delete_option_kwargs)
        else:
            self.delete_option_kwargs = {}