Add IM\Disk service for im.disk.folder.get

[mesilov]

Problem

The Bitrix24 REST API method im.disk.folder.get (id of the disk folder where chat files are stored) is not yet supported by the SDK.

Proposed solution

Add a new service src/Services/IM/Disk/Service/Disk.php that wraps the REST method below, following patterns in other src/Services/<Scope>/ folders. Scope: im.

Methods to implement

• im.disk.folder.get — id of the folder where chat files are stored

Acceptance criteria

• Bitrix24\SDK\Services\IM\Disk\Service\Disk implements the method with correct parameter mapping and #[ApiEndpointMetadata] / #[ApiServiceMetadata(new Scope(['im']))] attributes
• IMServiceBuilder::disk() exposes the new service
• Unit tests in tests/Unit/Services/IM/Disk/Service/DiskTest.php pass (make test-unit)
• Integration tests in tests/Integration/Services/IM/Disk/Service/DiskTest.php pass
• make test-integration-im-disk target added to Makefile and a suite added to phpunit.xml.dist
• CHANGELOG.md entry under ## 3.2.0 – UNRELEASED → ### Added with link to this issue

Part of #422.