docs: add partition truncation tip to ALTER TABLE reference

[Oladele Oluwaseun (soepic1)]

Summary

Engineers coming from other database engines (like Oracle or MySQL) frequently attempt to run ALTER TABLE <table_name> TRUNCATE PARTITION <id> on SQL Server, which throws Msg 156: Incorrect syntax near the keyword 'TRUNCATE'.

This PR adds a brief [!TIP] callout under the Partition Management section of alter-table-transact-sql.md cross-referencing TRUNCATE TABLE ... WITH (PARTITIONS (...)) to improve discoverability and prevent syntax confusion.

Checklist

• Content is accurate and matches T-SQL syntax standards
• Formatted using standard Learn Markdown syntax (> [!TIP])
• Included relative link to truncate-table-transact-sql.md

[prmerger-automator]

Oladele Oluwaseun (@soepic1) : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[prmerger-automator]

Oladele Oluwaseun (@soepic1) : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit 2c2534f:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/t-sql/statements/alter-table-transact-sql.md	✅Succeeded

For more details, please refer to the build report.

[Regan Downer (v-regandowner)]

Mark Ghanayem (@markingmyname)

Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team