[SPARK-17138][ML][MLIB] Add Python API for multinomial logistic regression
[SPARK-17138][ML][MLIB] Add Python API for multinomial logistic regression

## What changes were proposed in this pull request?

Add Python API for multinomial logistic regression.

- add `family` param in python api.
- expose `coefficientMatrix` and `interceptVector` for `LogisticRegressionModel`
- add python-side testcase for multinomial logistic regression
- update python doc.

## How was this patch tested?

existing and added doc tests.

Author: WeichenXu <WeichenXu123@outlook.com>

Closes #14852 from WeichenXu123/add_MLOR_python.

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