docs: add documentation for passing references to L1s

[leonmk-aws]

Description

Documentation Change Type:

• Typo/grammar fix
• Clarification or minor improvement
• New example or code snippet
• New section or topic
• Major restructuring or enhancement

Affected Documentation Page(s):

https://docs.aws.amazon.com/cdk/v2/guide/constructs.html

Description of Changes

Adds a section explaining that L1s accept references to construct for some properties and an example on how to use it.

Motivation and Context

This functionality was newly added and was not documented.

How Has This Been Validated?

Previewed the changes locally with asciidoctor.

Screenshots (if appropriate)

Checklist

• My changes follow the AsciiDoc syntax guidelines
• I have previewed my changes using GitHub's preview or a local AsciiDoc renderer
• My changes maintain consistent formatting with the rest of the documentation
• I have checked that all links work correctly

Additional Information

[rix0rrr]

Maybe something more generic, like "referencing other resources from other resources".

Discuss the choices (string, object references).

Discuss that object references may not be available for all relationships, and that it depends on a knowledge base we have that gets updated periodically, so the availability may shift over time.

Make clear that object references are internally immediately converted to strings, so users will only see strings on the mutable properties.

Make clear that this feature only works for top-level properties currently.

[rix0rrr]

Did you check that this doesn't conflict with other sections, or no other sections need rewrites?

[leonmk-aws]

Updated based on your feedback, I didn't find any conflicts / rewrites needed.