Add getter for path field in NestedQueryBuilder

[psmagin]

Is your feature request related to a problem? Please describe.
The only way now to get path from NestedQueryBuilder is a reflection

[saratvemulapalli]

@psmagin thanks for opening up the issue. Trying to understand, what is the use case of using path?
Also on a side note, could you contribute the change? (It should be pretty straight forward)[1]

[1] https://github.com/opensearch-project/OpenSearch/blob/main/server/src/main/java/org/opensearch/index/query/NestedQueryBuilder.java

[psmagin]

@saratvemulapalli, it could be useful for creating some complicated queries, the path could be used as a key field to combine nested queries in one.