This commit adds a new field to the response of the terms aggregation called
`sum_other_doc_count` which is equal to the sum of the doc counts of the buckets
that did not make it to the list of top buckets. It is typically useful to have
a sector called eg. `other` when using terms aggregations to build pie charts.
Example query and response:
```json
GET test/_search?search_type=count
{
"aggs": {
"colors": {
"terms": {
"field": "color",
"size": 3
}
}
}
}
```
```json
{
[...],
"aggregations": {
"colors": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 4,
"buckets": [
{
"key": "blue",
"doc_count": 65
},
{
"key": "red",
"doc_count": 14
},
{
"key": "brown",
"doc_count": 3
}
]
}
}
}
```
Close#8213