Clarify supported CPU models for CPU templates

[zulinx86]

Changes

• Clarify supported CPU models for CPU template

Reason

The existing CPU templates won't support Intel Sapphire Rapids. Before adding it, let's make the documentation description clearer around what CPU models are supported for each CPU template.

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PR Checklist

• I have read and understand CONTRIBUTING.md.
• I have run tools/devtool checkstyle to verify that the PR passes the
  automated style checks.
• I have described what is done in these changes, why they are needed, and
  how they are solving the problem in a clear and encompassing way.
• I have updated any relevant documentation (both in code and in the docs)
  in the PR.
• I have mentioned all user-facing changes in CHANGELOG.md.
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---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 3 lines in your changes missing coverage. Please review.

Project coverage is 83.02%. Comparing base (8ce1360) to head (c8848a4).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
.../src/cpu_config/x86_64/static_cpu_templates/mod.rs	88.88%	2 Missing ⚠️
...c/vmm/src/cpu_config/x86_64/custom_cpu_template.rs	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5142      +/-   ##
==========================================
- Coverage   83.02%   83.02%   -0.01%     
==========================================
  Files         250      250              
  Lines       26911    26902       -9     
==========================================
- Hits        22344    22335       -9     
  Misses       4567     4567              

Flag	Coverage Δ
5.10-c5n.metal	83.56% <84.61%> (+0.01%)	⬆️
5.10-m5n.metal	83.56% <84.61%> (+0.01%)	⬆️
5.10-m6a.metal	82.78% <69.23%> (+0.07%)	⬆️
5.10-m6g.metal	79.36% <ø> (ø)
5.10-m6i.metal	83.55% <84.61%> (+0.01%)	⬆️
5.10-m7a.metal-48xl	82.77% <64.10%> (?)
5.10-m7g.metal	79.36% <ø> (ø)
6.1-c5n.metal	83.61% <84.61%> (+0.02%)	⬆️
6.1-m5n.metal	83.60% <84.61%> (+0.01%)	⬆️
6.1-m6a.metal	82.83% <69.23%> (+0.07%)	⬆️
6.1-m6g.metal	79.36% <ø> (ø)
6.1-m6i.metal	83.59% <84.61%> (+0.01%)	⬆️
6.1-m7a.metal-48xl	82.82% <64.10%> (?)
6.1-m7g.metal	79.36% <ø> (ø)

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[zulinx86]

@roypat sorry. I needed to fix an integration test failure that sets C3 template unconditionally on Intel Sapphire Rapids.