rpm2img: add source packages of sub-packages

[piyush-jena]

Description of changes:
Add source packages of sub-packages if the names don't match.

Testing
New entries added to application-inventory.json for ecs-2 variant:

1. amazon-ssm-agent for amazon-ssm-agent-plugin and amazon-ssm-agent-plugin-bin

    {
      "Name": "amazon-ssm-agent",
      "Publisher": "bottlerocket-core-kit",
      "Version": "3.3.3185.0",
      "Release": "1.1764962845.9b3a8b3a.br1",
      "Epoch": "0",
      "InstalledTime": "2025-12-12T23:05:49Z",
      "ApplicationType": "Unspecified",
      "Architecture": "x86_64",
      "Url": "https://github.com/aws/amazon-ssm-agent",
      "Summary": "bottlerocket-amazon-ssm-agent (source package)"
    },

2. microcode for microcode-amd-license

    {
      "Name": "microcode",
      "Publisher": "bottlerocket-kernel-kit",
      "Version": "0.0",
      "Release": "1.1762999032.6bbcd107.br1",
      "Epoch": "1",
      "InstalledTime": "2025-12-12T23:05:49Z",
      "ApplicationType": "Unspecified",
      "Architecture": "x86_64",
      "Url": "https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/LICENSE.amd-ucode",
      "Summary": "bottlerocket-microcode (source package)"
    },

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.