Update instructions for using Layout Analyzer in Microsoft Foundry

[v-vfarias]

This pull request updates the exercise instructions for using Azure Content Understanding analyzers in the Microsoft Foundry portal. The changes clarify navigation steps in the portal and update terminology to match the latest UI and feature names.

Portal navigation and terminology updates:

• Updated instructions to use the Services section and the Playgrounds tab instead of the previous Deployments and AI Services tabs for accessing prebuilt models in the Foundry portal (Instructions/Exercises/01-content-understanding.md).
• Changed references to the analyzer names to match the current UI, updating "Azure Content Understanding - Layout" to "Content Understanding - Document Layout Analyzer" (Instructions/Exercises/01-content-understanding.md).
• Clarified the terminology in the note, changing "Read" to "OCR/Read" and updating the description to reflect that both OCR/Read and Layout analyzers are available (Instructions/Exercises/01-content-understanding.md).
• Updated the optional step to refer to the "Services" tab and the "Azure Content Understanding - OCR/Read" analyzer, aligning with the new naming and navigation (Instructions/Exercises/01-content-understanding.md).