Update instructions for finding Dataverse skill ID

[pkbullock]

Updated instructions, as the location for finding this wasn't descriptive enough to find the right area of Copilot Studio to extract the definition. After recently running through the docs, there was a gap here and made it quite hard to work out how to set this up.

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This pull request updates the instructions for finding the unique skill identifier for Dataverse knowledge sources in the docs/includes/dataverse-knowledge-skill-location.md file. The steps now provide more detailed guidance, including agent selection and creation.

Documentation improvements:

• Expanded the step-by-step instructions to include finding the "Copilot for Microsoft 365" agent, creating a new agent, and then proceeding with the process to add and publish a Dataverse knowledge source, making the process clearer for users.