Please add support multiline label to sql_table shape

[KateFox1982]

Feature Request: Multiline Labels for sql_table Title

Summary

Enable multiline strings in the sql_table title/label.
This feature would improve readability and expressiveness when creating high-level data models, especially when using the new suspend / unsuspend functionality introduced in D2 v0.7.

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Problem / Motivation

Currently, the sql_table title supports only a single-line label.
However, when building conceptual or logical data models, it is often necessary to include:

• additional descriptions of the entity
• business context
• module or subsystem names
• indicators of how/where the model was generated (e.g., via suspend)
• metadata such as version, status, or classification

Without multiline labels in the table header, users must either clutter the diagram with separate comment nodes or omit important context.

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Proposed Solution

Allow the sql_table title to accept multiline strings, for example:

sql_table Users {
  label: "Users\n(Conceptual Model)"
}

or using | strings:

sql_table Users {
  label: |
Users
(Conceptual Model)
  |
}

Expected behavior:

• the table header expands vertically when multiline text is used
• all lines are rendered inside the header cell
• alignment remains consistent with existing themes
• exports (SVG/PNG) preserve multiline formatting

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Why This Should Be in Core

• Enables more expressive and readable data models.
• Matches expectations from ERD and data modeling tools.
• Complements the new suspend/unsuspend features introduced in D2 v0.7.
• Backwards-compatible and does not change current behavior.