[FLINK-40174][docs] Document the EARLY_FIRE hint for interval joins

[weiqingy]

Part of the FLIP-497 stack under umbrella FLINK-36953. Stacked on PR-6. Landing order: PR-1a → PR-1b → PR-2 → PR-3 → PR-4 → PR-5 → PR-6 → PR-7 (this).

What is the purpose of the change

Documents the EARLY_FIRE join hint for SQL interval joins in the user-facing docs.

Brief change log

• Add the EARLY_FIRE section to the join docs (EN + ZH): semantics (speculative null-padded emission and later correction), the target/delay/time-mode options, the outer-join-only scope, and the relationship to the table.exec.emit.* configuration.

Verifying this change

This change is documentation only.

• Verified the pages render and the option table lists target, delay, and time-mode.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no (documents the FLIP-497 hint)
• If yes, how is the feature documented? docs

---

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: Claude Code (Anthropic)