[SPARK-20506][DOCS] Add HTML links to highlight list in MLlib guide for 2.2
[SPARK-20506][DOCS] Add HTML links to highlight list in MLlib guide for 2.2

Quick follow up to #17996 - forgot to add the HTML links to the relevant sections of the guide in the highlights list.

## How was this patch tested?

Built docs locally and tested links.

Author: Nick Pentreath <nickp@za.ibm.com>

Closes #18043 from MLnick/SPARK-20506-2.2-migration-guide-2.

pgandhi999/spark,highfei2011/spark,ericvandenbergfb/spark,janewangfb/spark,andrewor14/spark,nlalevee/spark,highfei2011/spark,ericvandenbergfb/spark,mike0sv/spark,JoshRosen/spark,andrewor14/spark,jiangxb1987/spark,nilsgrabbert/spark,saltstar/spark,cloud-fan/spark,nchammas/spark,wangmiao1981/spark,vinodkc/spark,liutang123/spark,bravo-zhang/spark,rikima/spark,spark-test/spark,yanboliang/spark,rezasafi/spark,aosagie/spark,aray/spark,kissmetrics/spark,milliman/spark,dongjoon-hyun/spark,ahnqirage/spark,zuotingbing/spark,jiangxb1987/spark,adrian-ionescu/apache-spark,shubhamchopra/spark,hhbyyh/spark,ahnqirage/spark,JoshRosen/spark,narahari92/spark,cloud-fan/spark,nilsgrabbert/spark,bdrillard/spark,someorz/spark,hvanhovell/spark,shaneknapp/spark,SHASHANKB/spark,byakuinss/spark,highfei2011/spark,rednaxelafx/apache-spark,aosagie/spark,goldmedal/spark,gengliangwang/spark,huang1900/spark,tengpeng/spark,zuotingbing/spark,szhem/spark,maropu/spark,brad-kaiser/spark,HyukjinKwon/spark,srowen/spark,andrewor14/spark,caneGuy/spark,chuckchen/spark,icexelloss/spark,darionyaphet/spark,wangyum/spark,milliman/spark,witgo/spark,apache/spark,wzhfy/spark,1haodian/spark,ajaysaini725/spark,xflin/spark,liyichao/spark,markhamstra/spark,saltstar/spark,SHASHANKB/spark,lvdongr/spark,liyichao/spark,tejasapatil/spark,aray/spark,LantaoJin/spark,darionyaphet/spark,ron8hu/spark,jiangxb1987/spark,joseph-torres/spark,saturday-shi/spark,1haodian/spark,aray/spark,gengliangwang/spark,chuckchen/spark,goldmedal/spark,spark-test/spark,jkbradley/spark,dhruve/spark,michalsenkyr/spark,vinodkc/spark,chuckchen/spark,map222/spark,ptkool/spark,facaiy/spark,wangyum/spark,markhamstra/spark,lvdongr/spark,bOOm-X/spark,BryanCutler/spark,facaiy/spark,zhouyejoe/spark,LantaoJin/spark,pgandhi999/spark,zzcclp/spark,skonto/spark,dbtsai/spark,ioana-delaney/spark,JoshRosen/spark,ahnqirage/spark,mike0sv/spark,WeichenXu123/spark,icexelloss/spark,caneGuy/spark,mike0sv/spark,szhem/spark,jiangxb1987/spark,sureshthalamati/spark,saltstar/spark,poffuomo/spark,facaiy/spark,zhouyejoe/spark,apache/spark,bravo-zhang/spark,LantaoJin/spark,markhamstra/spark,ddna1021/spark,maropu/spark,zzcclp/spark,cin/spark,JoshRosen/spark,guoxiaolongzte/spark,narahari92/spark,ericvandenbergfb/spark,srowen/spark,zuotingbing/spark,ajaysaini725/spark,joseph-torres/spark,akopich/spark,someorz/spark,byakuinss/spark,aokolnychyi/spark,kevinyu98/spark,aokolnychyi/spark,tengpeng/spark,vinodkc/spark,minixalpha/spark,pgandhi999/spark,dhruve/spark,tejasapatil/spark,ioana-delaney/spark,ahnqirage/spark,zhouyejoe/spark,caneGuy/spark,witgo/spark,mdespriee/spark,dbtsai/spark,holdenk/spark,kissmetrics/spark,adrian-ionescu/apache-spark,shaneknapp/spark,esi-mineset/spark,JoshRosen/spark,gengliangwang/spark,eyalfa/spark,maropu/spark,yanboliang/spark,kevinyu98/spark,rekhajoshm/spark,ddna1021/spark,apache/spark,hvanhovell/spark,rikima/spark,akopich/spark,janewangfb/spark,holdenk/spark,taroplus/spark,rekhajoshm/spark,chuckchen/spark,HyukjinKwon/spark,janewangfb/spark,ptkool/spark,UndeadBaneGitHub/spark,hhbyyh/spark,shuangshuangwang/spark,1haodian/spark,dbtsai/spark,bOOm-X/spark,goldmedal/spark,ron8hu/spark,wzhfy/spark,kiszk/spark,nlalevee/spark,liutang123/spark,mdespriee/spark,HyukjinKwon/spark,ueshin/apache-spark,maropu/spark,janewangfb/spark,bOOm-X/spark,ueshin/apache-spark,ConeyLiu/spark,sahilTakiar/spark,eyalfa/spark,BryanCutler/spark,narahari92/spark,srowen/spark,aray/spark,WeichenXu123/spark,joseph-torres/spark,aokolnychyi/spark,minixalpha/spark,lxsmnv/spark,mahak/spark,rezasafi/spark,darionyaphet/spark,mzl9039/spark,wzhfy/spark,cloud-fan/spark,guoxiaolongzte/spark,byakuinss/spark,mahak/spark,ConeyLiu/spark,apache/spark,ueshin/apache-spark,guoxiaolongzte/spark,facaiy/spark,minixalpha/spark,aokolnychyi/spark,dhruve/spark,saturday-shi/spark,vinodkc/spark,lvdongr/spark,byakuinss/spark,loneknightpy/spark,wangmiao1981/spark,eyalfa/spark,yanboliang/spark,ddna1021/spark,zzcclp/spark,kevinyu98/spark,Aegeaner/spark,lxsmnv/spark,kiszk/spark,michalsenkyr/spark,huang1900/spark,shuangshuangwang/spark,ptkool/spark,aosagie/spark,vinodkc/spark,facaiy/spark,lxsmnv/spark,sahilTakiar/spark,mike0sv/spark,pgandhi999/spark,eyalfa/spark,someorz/spark,poffuomo/spark,caneGuy/spark,kevinyu98/spark,tejasapatil/spark,srowen/spark,kissmetrics/spark,stanzhai/spark,rezasafi/spark,andrewor14/spark,zhouyejoe/spark,holdenk/spark,sureshthalamati/spark,dongjoon-hyun/spark,stanzhai/spark,shuangshuangwang/spark,goldmedal/spark,ConeyLiu/spark,setjet/spark,chuckchen/spark,liyichao/spark,sureshthalamati/spark,1haodian/spark,zzcclp/spark,poffuomo/spark,ptkool/spark,skonto/spark,bOOm-X/spark,aokolnychyi/spark,someorz/spark,ron8hu/spark,rezasafi/spark,aokolnychyi/spark,saltstar/spark,shubhamchopra/spark,sureshthalamati/spark,andrewor14/spark,zero323/spark,joseph-torres/spark,liyichao/spark,sahilTakiar/spark,huang1900/spark,loneknightpy/spark,xuanyuanking/spark,UndeadBaneGitHub/spark,saturday-shi/spark,mike0sv/spark,alunarbeach/spark,ron8hu/spark,sureshthalamati/spa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