Add how-to docs for Private Links, Private Endpoints, and NSP Configuration operations

[Copilot]

New how-to documentation for the standard ARM operation templates covering private networking scenarios. These templates exist in typespec-azure-resource-manager with samples but had no user-facing guides.

Three new pages under website/src/content/docs/docs/howtos/ARM/:

• private-links.md — PrivateLink model + PrivateLinks<> interface (Read, ListByParent)
• private-endpoints.md — PrivateEndpointConnectionResource model + PrivateEndpoints<> interface (full CRUD: Read, CreateOrUpdateAsync, CustomPatchAsync, DeleteAsync, ListByParent, plus sync variants)
• network-security-perimeter.md — NspConfiguration model + NspConfigurations<> interface (Read, ListByParent, Action, ActionAsync), with a note on the v5 common-types minimum

Each doc covers: resource model definition → operations alias setup → wiring into @armResourceOperations interface → available operations table → complete example → child resource reuse pattern.

// Pattern shown in each doc
model PrivateEndpointConnection is PrivateEndpointConnectionResource;
alias PrivateEndpointOps = PrivateEndpoints<PrivateEndpointConnection>;

@armResourceOperations
interface Employees {
  getConnection is PrivateEndpointOps.Read<Employee>;
  createConnection is PrivateEndpointOps.CreateOrUpdateAsync<Employee>;
  deleteConnection is PrivateEndpointOps.DeleteAsync<Employee>;
  listConnections is PrivateEndpointOps.ListByParent<Employee>;
}

Pages auto-appear in the sidebar via the existing autogenerate config for the howtos directory.

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[azure-sdk]

No changes needing a change description found.

[markcowl]

/azp run typespec-azure - CI

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[azure-sdk]

You can try these changes here

🛝 Playground	🌐 Website

[timotheeguerin]

Is that a copy of one of our examples? One thing I wanted to do as well with the examples is provide a

so we don't have dup and out dated examples

[markcowl]

It isn't precisely a copy (in either case) because it uses ListByParent instead of ListSinglePageByParent, but what would be the right format to include a reference to the playground sample? SHould we wait until your PR is merged/

[timotheeguerin]

there isn't right now but if we want to have that it should be easy to add, just wanted to keep track of the samples to replace if we add it.
Created an issue if you can add what sample it would be and where so we can replace after #3968 you think its valuable for this one)

[timotheeguerin]

Same here