DOC: Update installation instructions following changes in ecosystem

[david-cortes-intel]

Description

This PR updates the installation instructions:

• It removes references to the Intel distribution of Python, which is no longer offered (now it's just packages, not a python installer).
• It remove references to the AI kit, which is no longer available.
• It updates the instructions to not suggest Intel's channels as the first recommendation anymore, since by now the builds there do not have any advantage over the ones in PyPI and conda-forge.

---

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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[ethanglaser]

To me it makes sense to leave this tip below the section describing GPU and spmd support configurations

[david-cortes-intel]

It's still there. This PR is moving it it upwards.

[ethanglaser]

Same comment as above