Preserve overrides with export and import

[Trenly]

• I have signed the Contributor License Agreement.
• I have updated the Release Notes.
• This pull request is related to an issue.
  • Enhance import/export schema to include override values #1512

Summary

When a package is installed with --override or --custom arguments, those values are now preserved through the winget export / winget import roundtrip, allowing packages to be reinstalled with the same
customizations automatically.

Changes

Export (winget export)

• The installed package metadata is queried for previously stored UserOverrideArguments and UserCustomSwitches values and written into the export file under the new OverrideArguments and CustomSwitches
  fields per package entry.
• The packages schema v2.0 has been updated to define both new optional fields.

Import (winget import)

• When processing packages from an import file, OverrideArguments and CustomSwitches are now forwarded as --override and --custom args respectively into each package's install sub-context.
• Both fields are fully independent and optional — packages without them are unaffected.

Install metadata persistence

• --override and --custom values supplied at install time are now stored in the package's installed metadata (UserOverrideArguments / UserCustomSwitches), making them available for future export
  operations and upgrade flows.

Tests

• PackageCollection unit tests covering serialization and deserialization of OverrideArguments and CustomSwitches in both the v2.0 schema parser and JSON writer, including cases where either, both, or
  neither field is present.
• ExportFlow unit tests verifying that installed packages with stored override/custom metadata produce the correct fields in the export file.
• CompositeSource unit tests covering propagation of UserOverrideArguments and UserCustomSwitches metadata.
• ImportFlow unit tests (ImportFlow_WithOverrideArgs, ImportFlow_WithCustomSwitches) verifying that each field is independently applied during install — override args replace all installer arguments while
  custom switches are appended alongside the defaults.

---

Microsoft Reviewers: Open in CodeFlow