Adjust FieldExtractor to handle fields which contain `.` in their
name, regardless where they fall in, in the document hierarchy. E.g.:
```
{
"a.b": "Elastic Search"
}
{
"a": {
"b.c": "Elastic Search"
}
}
{
"a.b": {
"c": {
"d.e" : "Elastic Search"
}
}
}
```
Fixes: #37128