fix(docs): Fix missing modal size auto

[tienvx]

Description

I notice the size auto is available for modaland confirm components (based on the default value of sizesConfig). But it's not documented. So I added it to the size list. Also I fix the size in a modal's example, where it was small, but it should be auto

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any feature but make things better)

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