DOC: Instructions for verifying GPU support

[david-cortes-intel]

Description

This PR adds a section with instructions to verify that devices are recognized by sycl.

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Checklist:

Completeness and readability

• I have updated the documentation to reflect the changes or created a separate PR with updates and provided its number in the description, if necessary.
• Git commit message contains an appropriate signed-off-by string (see CONTRIBUTING.md for details).
• I have resolved any merge conflicts that might occur with the base branch.

Testing

• I have run it locally and tested the changes extensively.
• All CI jobs are green or I have provided justification why they aren't.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[david-cortes-intel]

Failing CI should be solved with this PR:
#2935