[FEATURE] Support multiple collapse inner hits

[luisovidio]

Is your feature request related to a problem?

OpenSearch-Net doesn't allow multiple collapse inner hits. This was developed for the Java client 8 years ago already.

What solution would you like?

Allow https://github.com/opensearch-project/opensearch-net/blob/main/src/OpenSearch.Client/Search/Search/Collapsing/FieldCollapse.cs to receive multiple InnerHits

Do you have any additional context?

opensearch-project/OpenSearch@601a61a

[andrross]

Catch All Triage - 1 2

@luisovidio Any interest in creating a PR to fix this?

[luisovidio]

@andrross, It is on my plans, yes.

Just need to find time/motivation