[Star tree] star tree off heap changes

[bharath-techie]

Is your feature request related to a problem? Please describe

Sort and aggregation of segment documents when building star tree takes up lots of resources if they are stored in in-memory structures like Lists. So this issue tracks the off heap implementation where we store and retrieve the star tree documents in off heap method using temporary files.

Describe the solution you'd like

We will store the offsets in array and swap the offsets when we go through the files. We offload the entire sort and aggregation of segment documents and construction of star tree documents to off-heap.

Related component

Other

Describe alternatives you've considered

No response

Additional context

No response

[peternied]

[Triage - attendees 1 2]
@bharath-techie Thanks for creating this issue, it looks like this should be related to the indexing area.