[DOCS] Added important updateStateByKey details
[DOCS] Added important updateStateByKey details

Runs for *all* existing keys and returning "None" will remove the key-value pair.

Author: Michael Vogiatzis <michaelvogiatzis@gmail.com>

Closes #7229 from mvogiatzis/patch-1 and squashes the following commits:

e7a2946 [Michael Vogiatzis] Updated updateStateByKey text
00283ed [Michael Vogiatzis] Removed space
c2656f9 [Michael Vogiatzis] Moved description farther up
0a42551 [Michael Vogiatzis] Added important updateStateByKey details

vinodkc/spark,techaddict/spark,actuaryzhang/spark,darionyaphet/spark,shuangshuangwang/spark,srowen/spark,dongjoon-hyun/spark,nchammas/spark,xuanyuanking/spark,jkbradley/spark,holdenk/spark,alunarbeach/spark,andrewor14/spark,aosagie/spark,zhouyejoe/spark,jiangxb1987/spark,ajaysaini725/spark,darionyaphet/spark,JoshRosen/spark,dongjoon-hyun/spark,saturday-shi/spark,nchammas/spark,mzl9039/spark,jkbradley/spark,tejasapatil/spark,WeichenXu123/spark,rednaxelafx/apache-spark,holdenk/spark,shaneknapp/spark,srowen/spark,ahnqirage/spark,aosagie/spark,michalsenkyr/spark,taroplus/spark,hvanhovell/spark,kevinyu98/spark,wangmiao1981/spark,spark-test/spark,shuangshuangwang/spark,aray/spark,icexelloss/spark,huang1900/spark,shubhamchopra/spark,poffuomo/spark,alunarbeach/spark,SnappyDataInc/spark,zuotingbing/spark,ueshin/apache-spark,cloud-fan/spark,rezasafi/spark,pgandhi999/spark,sureshthalamati/spark,wangyum/spark,zuotingbing/spark,icexelloss/spark,eyalfa/spark,spark-test/spark,rikima/spark,rikima/spark,pronix/spark,publicRoman/spark,witgo/spark,shubhamchopra/spark,jlopezmalla/spark,minixalpha/spark,1haodian/spark,ericvandenbergfb/spark,guoxiaolongzte/spark,jrshust/spark,map222/spark,guoxiaolongzte/spark,srowen/spark,alunarbeach/spark,zero323/spark,szhem/spark,ibm-research-ireland/sparkoscope,mzl9039/spark,someorz/spark,UndeadBaneGitHub/spark,tengpeng/spark,chuckchen/spark,cin/spark,cin/spark,markhamstra/spark,joseph-torres/spark,joseph-torres/spark,SHASHANKB/spark,narahari92/spark,mahak/spark,skonto/spark,saltstar/spark,sureshthalamati/spark,markhamstra/spark,bOOm-X/spark,SHASHANKB/spark,stanzhai/spark,jiangxb1987/spark,HyukjinKwon/spark,ioana-delaney/spark,stanzhai/spark,JerryLead/spark,haowu80s/spark,zuotingbing/spark,xuanyuanking/spark,haowu80s/spark,spark-test/spark,apache/spark,debugger87/spark,taroplus/spark,byakuinss/spark,ueshin/apache-spark,UndeadBaneGitHub/spark,apache/spark,facaiy/spark,Panos-Bletsos/spark-cost-model-optimizer,gioenn/xSpark,poffuomo/spark,someorz/spark,kiszk/spark,taroplus/spark,guoxiaolongzte/spark,patrick-nicholson/spark,pronix/spark,lxsmnv/spark,esi-mineset/spark,kiszk/spark,ibm-research-ireland/sparkoscope,wzhfy/spark,witgo/spark,spark-test/spark,JoshRosen/spark,bdrillard/spark,stanzhai/spark,setjet/spark,kiszk/spark,cin/spark,kimoonkim/spark,cloud-fan/spark,saltstar/spark,apache-spark-on-k8s/spark,gioenn/xSpark,poffuomo/spark,mike0sv/spark,SnappyDataInc/spark,goldmedal/spark,xflin/spark,actuaryzhang/spark,sachintyagi22/spark,zhouyejoe/spark,dbtsai/spark,brad-kaiser/spark,apache/spark,bravo-zhang/spark,dhruve/spark,kevinyu98/spark,saturday-shi/spark,shaneknapp/spark,ptkool/spark,nchammas/spark,jlopezmalla/spark,lvdongr/spark,maropu/spark,esi-mineset/spark,patrick-nicholson/spark,wangmiao1981/spark,yanboliang/spark,nchammas/spark,caneGuy/spark,Panos-Bletsos/spark-cost-model-optimizer,shaneknapp/spark,michalsenkyr/spark,jianran/spark,SnappyDataInc/spark,vinodkc/spark,debugger87/spark,shaneknapp/spark,pronix/spark,cloud-fan/spark,huang1900/spark,zhouyejoe/spark,ptkool/spark,kissmetrics/spark,bdrillard/spark,sahilTakiar/spark,dhruve/spark,jkbradley/spark,ueshin/apache-spark,skonto/spark,adrian-ionescu/apache-spark,highfei2011/spark,Panos-Bletsos/spark-cost-model-optimizer,milliman/spark,nlalevee/spark,ptkool/spark,zuotingbing/spark,ddna1021/spark,skonto/spark,LantaoJin/spark,pgandhi999/spark,xflin/spark,liyichao/spark,alunarbeach/spark,caneGuy/spark,tejasapatil/spark,nilsgrabbert/spark,gengliangwang/spark,SHASHANKB/spark,yanboliang/spark,JoshRosen/spark,sureshthalamati/spark,ericvandenbergfb/spark,jrshust/spark,ericvandenbergfb/spark,poffuomo/spark,esi-mineset/spark,tengpeng/spark,kissmetrics/spark,aokolnychyi/spark,cloud-fan/spark,liutang123/spark,cin/spark,dbtsai/spark,ajaysaini725/spark,zuotingbing/spark,rekhajoshm/spark,eyalfa/spark,SHASHANKB/spark,kimoonkim/spark,publicRoman/spark,ueshin/apache-spark,lxsmnv/spark,jkbradley/spark,panfengfeng/spark,BryanCutler/spark,rekhajoshm/spark,jrshust/spark,zhouyejoe/spark,ioana-delaney/spark,ron8hu/spark,ericvandenbergfb/spark,ajaysaini725/spark,chuckchen/spark,BryanCutler/spark,wzhfy/spark,apache/spark,metamx/spark,gengliangwang/spark,liyichao/spark,dhruve/spark,haowu80s/spark,poffuomo/spark,apache-spark-on-k8s/spark,mike0sv/spark,facaiy/spark,WeichenXu123/spark,jlopezmalla/spark,wangyum/spark,srowen/spark,markhamstra/spark,bOOm-X/spark,byakuinss/spark,facaiy/spark,kiszk/spark,dbtsai/spark,narahari92/spark,janewangfb/spark,map222/spark,nlalevee/spark,gengliangwang/spark,ptkool/spark,darionyaphet/spark,rednaxelafx/apache-spark,ahnqirage/spark,esi-mineset/spark,UndeadBaneGitHub/spark,poffuomo/spark,stanzhai/spark,shubhamchopra/spark,zhouyejoe/spark,hhbyyh/spark,aray/spark,ueshin/apache-spark,Aegeaner/spark,metamx/spark,holdenk/spark,zzcclp/spark,someorz/spark,rekhajoshm/spark,UndeadBaneGitHub/spark,shaneknapp/spark,tejasapatil/spark,stanzhai/spark,rikima/spark,kiszk/spark,huang1900/spark,markhamstra/spark,minixalpha/spark,lvdongr/spark,bravo-zhang/spark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