Update docs for GPU support with KVM

[vishesh92]

To be merged after: apache/cloudstack#11143

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📚 Documentation preview 📚: https://cloudstack-documentation--526.org.readthedocs.build/en/526/

[Copilot]

Pull Request Overview

This PR enhances the GPU support documentation by adding KVM-specific instructions, updating XenServer sections, introducing new service offering parameters, and extending usage/resource limits.

• Add KVM GPU passthrough and vGPU configuration details alongside existing XenServer guidance
• Introduce GPU Count and GPU Display options in compute offering docs
• Extend resource limit settings with GPU quotas and add host GPU discovery instructions

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
source/adminguide/virtual_machines.rst	Add KVM GPU passthrough/vGPU info and reorganize GPU sections
source/adminguide/usage.rst	Add max.account.gpus / max.project.gpus and detach-on-stop note
source/adminguide/service_offerings.rst	Rename GPU fields, add GPU Count & GPU Display options
source/adminguide/hosts.rst	Add “Discovering GPU Devices on Hosts” section

Comments suppressed due to low confidence (6)

source/adminguide/virtual_machines.rst:1597

• This paragraph appears as plain text rather than a list item; prefix it with '-' to maintain bulleted list consistency.

For KVM, CloudStack leverages libvirt's PCI passthrough feature to assign a

source/adminguide/virtual_machines.rst:1620

• [nitpick] Rename this heading to 'GPU passthrough' for clarity and consistency with earlier terminology.

**vGPU**: vGPU enables multiple Instances to share a single physical GPU.

source/adminguide/virtual_machines.rst:1633

• [nitpick] Use 'and' instead of '&' for readability, e.g., '(Supports only XenServer and KVM)'.

  (Supports only XenServer & KVM)

source/adminguide/usage.rst:252

• [nitpick] Consider aligning the new 'max.account.gpus' entry with the existing naming and ordering of resource limits for consistency.

max.account.gpus                    Maximum number of GPUs that can be used for an Account.

source/adminguide/service_offerings.rst:292

• [nitpick] Term 'GPU Card' differs from previous 'GPU'; consider using consistent terminology or clarifying the distinction.

   -  **GPU Card**: Assign a physical GPU(GPU-passthrough) or a portion of a physical

source/adminguide/hosts.rst:231

• Use 'CloudStack agent' instead of 'cloudstack agent' to maintain product name capitalization.

For KVM, the user needs to ensure that IOMMU is enabled and the necessary