Need 4 config "zkDigestUsername"/"zkDigestPassword"/"zkDigestReadonlyUsername"/"zkDigestReadonlyUsername" in solr.xml

Need 4 config in <solrhome>/solr.xml instead of -D parameter in solr.in.sh.

like below:
<solr>
<solrcloud>
<str name="zkDigestUsername">zkusername</str>
<str name="zkDigestPassword">zkpassword</str"zkDigestUsername">
<str name="zkDigestReadonlyUsername">zkreadonlyusername</str>
<str name="zkDigestReadonlyUsername">readonlypassword</str"zkDigestUsername">
...

Otherwise, any user can use the linux "ps" command showing the full command line including the plain text zookeeper username and password. If we use file store them, we can control the access of the file not to leak the username/password.