[ML] [Pipelines] perf optimization: resolve all leaf node concurrently

[elliotzh]

Description

update the function to divide nodes in a pipeline component into layers and put all leaf nodes (potentially involve slow operations like IO, file uploading and artifact downloading) at the last layer.

In this way, all slow operations can be done concurrently so improve the overall performance.

L2 first submission perf: 446s =>320s

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

API changes are not detected in this pull request.