[SPARK-33006][K8S][DOCS] Add dynamic PVC usage example into K8s doc
[SPARK-33006][K8S][DOCS] Add dynamic PVC usage example into K8s doc

### What changes were proposed in this pull request?

This updates K8s document to describe new dynamic PVC features.

### Why are the changes needed?

This will help the user use the new features easily.

### Does this PR introduce _any_ user-facing change?

Yes, but it's a doc updates.

### How was this patch tested?

Manual.

<img width="847" alt="Screen Shot 2020-09-28 at 3 54 53 PM" src="https://user-images.githubusercontent.com/9700541/94494923-3ed04400-01a5-11eb-81f9-127db42d4256.png">

<img width="779" alt="Screen Shot 2020-09-28 at 3 55 07 PM" src="https://user-images.githubusercontent.com/9700541/94494930-4394f800-01a5-11eb-9387-50ebc14af477.png">

Closes #29897 from dongjoon-hyun/SPARK-33006.

Authored-by: Dongjoon Hyun <9b02cb7e37158797a8e22c559f7c5f5ecd28ea57@apple.com>
Signed-off-by: Dongjoon Hyun <9b02cb7e37158797a8e22c559f7c5f5ecd28ea57@apple.com>

BryanCutler/spark,chuckchen/spark,maropu/spark,cloud-fan/spark,nchammas/spark,HyukjinKwon/spark,wangyum/spark,srowen/spark,shaneknapp/spark,xuanyuanking/spark,milliman/spark,witgo/spark,gengliangwang/spark,witgo/spark,wangmiao1981/spark,maropu/spark,taroplus/spark,dongjoon-hyun/spark,shuangshuangwang/spark,milliman/spark,wangyum/spark,witgo/spark,holdenk/spark,apache/spark,holdenk/spark,vinodkc/spark,jiangxb1987/spark,srowen/spark,ueshin/apache-spark,nchammas/spark,wangyum/spark,maropu/spark,apache/spark,HyukjinKwon/spark,zzcclp/spark,chuckchen/spark,chuckchen/spark,hvanhovell/spark,BryanCutler/spark,cloud-fan/spark,jiangxb1987/spark,witgo/spark,chuckchen/spark,ueshin/apache-spark,gengliangwang/spark,HyukjinKwon/spark,cloud-fan/spark,maropu/spark,zero323/spark,zero323/spark,shaneknapp/spark,shaneknapp/spark,dongjoon-hyun/spark,witgo/spark,ueshin/apache-spark,xuanyuanking/spark,JoshRosen/spark,taroplus/spark,rednaxelafx/apache-spark,jiangxb1987/spark,JoshRosen/spark,shaneknapp/spark,shuangshuangwang/spark,HyukjinKwon/spark,taroplus/spark,cloud-fan/spark,wangmiao1981/spark,shuangshuangwang/spark,wangyum/spark,apache/spark,shaneknapp/spark,zzcclp/spark,chuckchen/spark,vinodkc/spark,WeichenXu123/spark,BryanCutler/spark,holdenk/spark,taroplus/spark,nchammas/spark,rednaxelafx/apache-spark,srowen/spark,zero323/spark,zero323/spark,witgo/spark,milliman/spark,vinodkc/spark,zzcclp/spark,nchammas/spark,rednaxelafx/apache-spark,ueshin/apache-spark,wangyum/spark,HyukjinKwon/spark,xuanyuanking/spark,chuckchen/spark,wangmiao1981/spark,hvanhovell/spark,zero323/spark,xuanyuanking/spark,milliman/spark,HyukjinKwon/spark,maropu/spark,mahak/spark,apache/spark,nchammas/spark,cloud-fan/spark,WeichenXu123/spark,WeichenXu123/spark,taroplus/spark,vinodkc/spark,apache/spark,holdenk/spark,chuckchen/spark,cloud-fan/spark,gengliangwang/spark,WeichenXu123/spark,JoshRosen/spark,ueshin/apache-spark,BryanCutler/spark,wangmiao1981/spark,JoshRosen/spark,hvanhovell/spark,jiangxb1987/spark,BryanCutler/spark,dongjoon-hyun/spark,holdenk/spark,holdenk/spark,maropu/spark,zero323/spark,srowen/spark,cloud-fan/spark,jiangxb1987/spark,dongjoon-hyun/spark,HyukjinKwon/spark,holdenk/spark,dongjoon-hyun/spark,shuangshuangwang/spark,zzcclp/spark,milliman/spark,BryanCutler/spark,mahak/spark,gengliangwang/spark,jiangxb1987/spark,mahak/spark,wangmiao1981/spark,mahak/spark,zzcclp/spark,WeichenXu123/spark,ueshin/apache-spark,dongjoon-hyun/spark,shaneknapp/spark,srowen/spark,shuangshuangwang/spark,maropu/spark,wangyum/spark,shuangshuangwang/spark,rednaxelafx/apache-spark,taroplus/spark,ueshin/apache-spark,wangmiao1981/spark,jiangxb1987/spark,milliman/spark,gengliangwang/spark,zero323/spark,wangyum/spark,rednaxelafx/apache-spark,vinodkc/spark,mahak/spark,apache/spark,shuangshuangwang/spark,mahak/spark,wangmiao1981/spark,shaneknapp/spark,taroplus/spark,srowen/spark,nchammas/spark,gengliangwang/spark,JoshRosen/spark,milliman/spark,apache/spark,zzcclp/spark,hvanhovell/spark,JoshRosen/spark,mahak/spark,dongjoon-hyun/spark,xuanyuanking/spark,vinodkc/spark,hvanhovell/spark,nchammas/spark,BryanCutler/spark,WeichenXu123/spark,zzcclp/spark,JoshRosen/spark,gengliangwang/spark,hvanhovell/spark,WeichenXu123/spark,rednaxelafx/apache-spark,hvanhovell/spark,vinodkc/spark,srowen/spark,xuanyuanking/spark,xuanyuanking/spark,rednaxelafx/apache-spark,witgo/spark