Add Maximum Upload Size customisation notes.

[Duncan-Cloudflare]

See SPM-2839 for details.

[hyperlint-ai]

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PR Change Summary

Added customization notes regarding the Maximum Upload Size feature in the documentation.

• Introduced notes on reducing the Maximum Upload Size from the zone's Network page.
• Clarified the implications of exceeding the Maximum Upload Size, including potential 413 errors.

Modified Files

• src/content/docs/cache/concepts/default-cache-behavior.mdx
• src/content/docs/support/troubleshooting/http-status-codes/4xx-client-error.mdx

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