[Avocado] Support service group folder scenario

[raych1]

Avocado cannot identify the readme under service group folder. There're more and more services using service group folder structure and tooling should extend the support for this scenario.

Rule | Message
-- | --
❌ MISSING_README | Can not find readme.md in the folder. If no readme.md file, it will block SDK generation.folder: Microsoft.Quantum/preview/2019-11-04-preview/examples
❌ MISSING_README | Can not find readme.md in the folder. If no readme.md file, it will block SDK generation.folder: resource-manager/Microsoft.Quantum/preview/2019-11-04-preview
❌ MISSING_README | Can not find readme.md in the folder. If no readme.md file, it will block SDK generation.folder: d04a75907d3e0afd2e12b27a579867d538656f9f/specification/quantum/resource-manager

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</body>
</html>Rule	Message
❌ [MISSING_README](https://github.com/Azure/avocado/blob/master/README.md#MISSING_README)	Can not find readme.md in the folder. If no readme.md file, it will block SDK generation.
folder: [Microsoft.Quantum/preview/2019-11-04-preview/examples](https://github.com/Azure/azure-rest-api-specs-pr/blob/d04a75907d3e0afd2e12b27a579867d538656f9f/specification/quantum/resource-manager/Microsoft.Quantum/preview/2019-11-04-preview/examples)
❌ [MISSING_README](https://github.com/Azure/avocado/blob/master/README.md#MISSING_README)	Can not find readme.md in the folder. If no readme.md file, it will block SDK generation.
folder: [resource-manager/Microsoft.Quantum/preview/2019-11-04-preview](https://github.com/Azure/azure-rest-api-specs-pr/blob/d04a75907d3e0afd2e12b27a579867d538656f9f/specification/quantum/resource-manager/Microsoft.Quantum/preview/2019-11-04-preview)
❌ [MISSING_README](https://github.com/Azure/avocado/blob/master/README.md#MISSING_README)	Can not find readme.md in the folder. If no readme.md file, it will block SDK generation.
folder: [d04a75907d3e0afd2e12b27a579867d538656f9f/specification/quantum/resource-manager](https://github.com/Azure/azure-rest-api-specs-pr/blob/d04a75907d3e0afd2e12b27a579867d538656f9f/specification/quantum/resource-manager)

This is an example PR.
https://github.com/Azure/azure-rest-api-specs-pr/pull/12613
//CC: @weshaggard @konrad-jamrozik

[konrad-jamrozik]

Relevant Teams discussion.

[konrad-jamrozik]

Another relevant Teams discussion.

[konrad-jamrozik]

This is relevant to:

• Develop semantic model of specs repo dir structure azure-sdk-tools#8203