It is very easy to sign your apk file using ionic. Go to platform -> android and keep your keystore file and release-signing.properties file. The release signing.properties file should be like
storeFile=***.keystore
keyAlias=***
storePassword=****
keyPassword=****
after that you need to build with this command
ionic build android --prod --release
then signed apk is generated in your apk folder. You dont need to execute jarsigner command every time. Just execute above command to sign apk file.After that put your apk file in latest build tools folder and zipalign it using
zipalign -v 4 {signed apk file name}.apk {output file name}.apk
then upload your output apk file into playstore