docs: turbopuffer sink

[maheshwarip]

Rebuilds #38167 with its CI failure fixed. Carries the original docs: turbopuffer sink commit unchanged, plus one commit that strips the trailing whitespace failing lint.

The fix can also be cherry-picked onto the original branch instead of merging this PR: git cherry-pick 88239bf.

Motivation

The buildkite/test/lint-and-rustfmt step on #38167 fails. That step runs bin/lint, whose check-whitespace.sh check rejects trailing whitespace via git diff --check:

doc/user/content/serve-results/sink/turbopuffer.md:16: trailing whitespace.
doc/user/content/serve-results/sink/turbopuffer.md:17: trailing whitespace.
doc/user/content/serve-results/sink/turbopuffer.md:18: trailing whitespace.

Every other check on #38167 passes, including lint-docs, preview-docs, and run-docs-js-widgets-tests.

Description

Three consecutive lines of the new turbopuffer sink guide ended with a single trailing space. Removing them is the whole fix. A lone trailing space is not a Markdown hard line break (that needs two or more), so the rendered page is byte-for-byte identical.

No content, wording, or structure was changed in the guide.

Verification

Reproduced the exact CI failure locally by running the script the failing step invokes, then confirmed it passes after the fix:

$ ci/test/lint-main/checks/check-whitespace.sh
--- xargs misc/lint/trailing-newline.py
--- xargs git --no-pager diff --check 4b825dc642cb6eb9a060e54bf8d69288fbee4904
+++ Status report
2/2 commands passed

The remaining bin/lint checks that fail in this environment (check-cargo, check-formatting, check-generation, check-protobuf, check-trufflehog, check-zizmor, check-helm-docs, check-python-docs) fail for missing local tooling (buf, cargo-deny, cargo-deplint, an older local rustc) and are unrelated to this docs-only diff. check-copyright, check-python-files, check-slack-links, and check-test-flags pass.

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