Enhance body streaming documentation in Request Data section

[coderabbitai]

Context

This issue tracks a suggestion made during review of PR #342.

Suggestion by @SandPod:

Mention body here as well since you can stream the body as well.

File: docs/06-concepts/18-webserver/03-request-data.md

Reference:

• PR: docs: Add documentation for Serverpod 3 WebServer" #342
• Comment: docs: Add documentation for Serverpod 3 WebServer" #342 (comment)
• Requested by: @nielsenko

Description

Consider enhancing the documentation to make body streaming more prominent or mention it in additional relevant sections of the Request Data documentation.