Add legacy note for spill to disk

[mosabua]

Description

This keeps coming up... might as well make it official.

Additional context and related issues

https://trinodb.slack.com/archives/CLEDR9V7G/p1722011311628259

Release notes

(x) This is not user-visible or is docs only, and no release notes are required.

[mosabua]

FTE is not really a replacement but solves the memory issue that spilling attempts to solve.

[wendigo]

@mosabua yeah, and we should probably start removing spilling logic as it's complex and broken anyway

[mosabua]

@mosabua yeah, and we should probably start removing spilling logic as it's complex and broken anyway

Sounds good. Wdyt @martint @dain @electrum - maybe we should create a roadmap issue and proceed?

[mosabua]

Here is the roadmap item - #22845

[losipiuk]

@mosabua yeah, and we should probably start removing spilling logic as it's complex and broken anyway

complex - yeah. Broken????

We wanted to remove it from join some time ago - but athena is heavy user so we left forked operator.

cc: @pettyjamesm

[wendigo]

@losipiuk i recall some user reported issues that we left unanswered as we don't want to invest into spilling anymore

[sopel39]

@losipiuk i recall some user reported issues that we left unanswered as we don't want to invest into spilling anymore

I don't think it's broken. It's also easier to deploy and has perf advantages as of now. I have second thoughts about removing it TBH.