Docs: move HA subsections to a deeper indentation level
Docs: move HA subsections to a deeper indentation level

Makes the table of contents read better

Author: Andrew Ash <andrew@andrewash.com>

Closes #2402 from ash211/docs/better-indentation and squashes the following commits:

ea0e130 [Andrew Ash] Move HA subsections to a deeper indentation level

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