pinot-admin.sh has bash error processing IFS and PLUGINS_INCLUDE env

Based on our latest test on latest master (this is probably there for a while)
That if we run the command with
`bash xxxxx/pinot-admin.sh` , and has `$PLUGINS_INCLUDE` defined, the below processing cannot get the plugins array properly:
```
IFS=';' echo "$PLUGINS_INCLUDE" | read -ra PLUGINS_ARR
```
I believe it is the file `src/main/resources/appAssemblerScriptTemplate`

We recently tested out the plugins_include macro and it works with trouble.

Start with src/main/resources/appAssemblerScriptTemplate and reproduce the reported command using bash xxxxx/pinot-admin.sh with PLUGINS_INCLUDE defined. Trace the IFS and PLUGINS_ARR handling; done means the plugins_include value is parsed into the expected plugins array.

Written by the indexing model from the issue text.