Correct Linux enterprise policy docs to use JSON examples (not plist XML)

[Copilot]

The Linux policy section states policies are read from /etc/vscode/policy.json, but its Step 2 examples were using macOS plist XML syntax, which is incompatible with JSON parsing. This updates the Linux examples to valid JSON and aligns the guidance with actual Linux policy file format.

• Scope

  • Updated Linux Step 2: Configure policy values in:
    • docs/enterprise/policies.md
    • docs/enterprise/policies.template.md

• What changed

  • Replaced plist-style XML key/value examples with a single valid policy.json example.
  • Removed XML-specific “delete key/value pair” wording and replaced it with JSON-property removal guidance.

• Resulting example

  {
    "AllowedExtensions": {"microsoft": true, "github": true},
    "UpdateMode": "start",
    "EnableFeedback": true,
    "EnableTelemetry": false
  }