feat: document shutdown config option for @astrojs/node

[WhatCats]

Description

Documents the new shutdown config option for the Node adapter, which controls graceful shutdown behavior (timeout and exit) when the standalone server receives SIGTERM/SIGINT.

References

• Related to feat(@astrojs/node): add graceful shutdown to standalone mode astro#17655
• For Astro version tbd
• Discord username: whatcats

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Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

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