[SPARK-28199][SPARK-28199][SS][FOLLOWUP] Mention the change of into the SS migration guide
[SPARK-28199][SPARK-28199][SS][FOLLOWUP] Mention the change of into the SS migration guide

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

SPARK-28199 (#24996) made the trigger related public API to be exposed only from static methods of Trigger class. This is backward incompatible change, so some users may experience compilation error after upgrading to Spark 3.0.0.

While we plan to mention the change into release note, it's good to mention the change to the migration guide doc as well, since the purpose of the doc is to collect the major changes/incompatibilities between versions and end users would refer the doc.

### Why are the changes needed?

SPARK-28199 is technically backward incompatible change and we should kindly guide the change.

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

Doc change.

### How was this patch tested?

N/A, as it's just a doc change.

Closes #28763 from HeartSaVioR/SPARK-28199-FOLLOWUP-doc.

Authored-by: Jungtaek Lim (HeartSaVioR) <6dfb5872701d21af1c4dd7add991df02fba61fbf@gmail.com>
Signed-off-by: Wenchen Fan <563f5923eae9a92c8a3f34a26b67fa348a303ed1@databricks.com>

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