Add preliminary support for ASR Model dataclasses
This pull request **introduces 1 alert** when merging cdb20c1742dca80fd3519991029d356e95573f98 into 9ea071605034f9f56db9b677eb1fe54fdee2b820 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-cc6090175340df7c3bed280609bfe623e3253748)

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* 1 for Unused import This pull request **introduces 1 alert** when merging 6ad69e3b240fe8ffedcaae7d4260dcbd05828c1b into 9ea071605034f9f56db9b677eb1fe54fdee2b820 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-2bbd5a3297d9a000e28efc1a91aba9366c42046e)

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# Changelog
- Adds nearly concrete implementations of dataclasses for QuartzNet 15x5, Jasper 10x5-DR and MatchboxNet-3x1x64 and VAD modes.
- Adds *ConfigBuilder class supporting the construction of arbitrarily complex interdependencies between sub-configs
- Adds various dataclasses for ASR datasets + ASR Classification datasets
- Adds core support for class-dataclass testing