docs: [branch-1.1] regenerate release docs for 1.1.0-rc2

[andygrove]

Which issue does this PR close?

N/A. This reruns the "Generate Release Documentation" step of the 1.1.0 release (#5327) for rc2. The first run, #6344, came before the backports that merged after rc1.

Rationale for this change

A release branch commits the generated docs under docs/source/user-guide/latest/, so the archived 1.1.0 docs render real tables. Some backports since #6344 change what the generator writes. #6488 added a config key, and #6489 and #6561 made the regr_* aggregates, array_distinct and array_union fall back to Spark by default. Without this, the 1.1.0 docs would leave out the new key and the reasons those expressions fall back.

What changes are included in this PR?

Output of ./dev/generate-release-docs.sh on branch-1.1 at 4f5cf2d, with no hand edits:

• configs.md: a row for spark.comet.exec.aggregate.skipPartial.enabled (fix: [branch-1.1] make adaptive aggregation skipping opt-in (#6474) #6488). The only other key added since docs: [branch-1.1] generate release docs for 1.1.0 #6344, spark.comet.testing.icebergWriteReport.dir (test: [branch-1.1] backport the Iceberg write report and the mid-write retry test (#6155, #6111) #6307), is internal, so the generator leaves it out.
• compatibility/expressions/spark-{3.4,3.5,4.0,4.1}/aggregate.md: why RegrIntercept, RegrR2, RegrReplacement, RegrSXY and RegrSlope fall back by default (fix: [branch-1.1] fall back for incompatible regression aggregates (#6451) #6489, the backport of fix: fall back to Spark for regr_* aggregates until their merge matches Spark #6451).
• compatibility/expressions/spark-{3.4,3.5,4.0,4.1}/array.md: why ArrayDistinct and ArrayUnion fall back by default for floating-point elements (fix: [branch-1.1] gate array distinct and union signed-zero semantics by Spark version (#5750) #6561, the backport of fix: gate array distinct and union signed-zero semantics by Spark version #5750).
• expressions.md: the Implementation column for regr_sxx and regr_syy goes back to the em-dash placeholder that docs: [branch-1.1] generate release docs for 1.1.0 #6344 generated. fix: [branch-1.1] fall back for incompatible regression aggregates (#6451) #6489 set it to "Native" when it added the fallback notes, which stay. The generator can't resolve these two rows because Spark rewrites both functions to RegrReplacement before Comet sees the plan, as docs: [branch-1.1] generate release docs for 1.1.0 #6344 describes.

The four Spark versions get the same additions.

How are these changes tested?

• ./dev/generate-release-docs.sh completed for all four Spark profiles on JDK 17.
• npx prettier@latest --check passes on the changed files.

[sunchao]

Summary

• Prior state and problem: The release docs omitted the partial-aggregation config and compatibility warnings added by recent backports.
• Design approach: Refresh committed documentation through the existing release-doc generator.
• Correctness / compatibility analysis: All 28 added compatibility sections match their source declarations. Checked relevant Spark sources for 3.4.3, 3.5.9, 4.0.4 and 4.1.3, plus the cited 4.2.0 normalization rule. No introduced P1/P2 issues found within this review.
• Key design decisions: Preserve explicit incompatible-expression opt-ins. The regr_sxx and regr_syy placeholders agree with the documented convention for expressions Spark rewrites. No new abstraction is introduced.
• Implementation sketch: Update eight compatibility pages, add one config row and refresh two implementation cells.
• Behavioral changes worth calling out: Documentation only, with no runtime or performance overhead. The config row accurately records the false default and potential shuffle amplification.
• Suggested improvements: None at P1/P2 priority.

Reviewed the full ten-file diff from 4f5cf2db1e80bf94db8a4b79a870738d621f1262 to bcf1a5f6c0abb554a45436832e444b906ee62495. Confirmed the PR is not a draft. The snapshot and live discussion endpoints contain no existing reviews or comments.

Routed skills: review-comet-pr. No sibling skill applies to this documentation-only change.

Exact-head CI: Label run / Preflight, label and check-pr-title succeeded. Preflight remains in progress and Label run / Detect changes is queued. No failures reported so far.

Validation: git diff --check and focused source-to-document consistency checks passed. Full Maven doc generation, Sphinx rendering and runtime suites were not rerun. Local Prettier validation was unavailable because npx is absent. CI is not yet complete.