feat: add transfer manager MPU sample, adjust defaults, prepare for GA

[ddelgrosso1]

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Fixes # 🦕

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 1 region tag.

- [samples/uploadFileInChunksWithTransferManager.js:28](https://github.com/ddelgrosso1/nodejs-storage/blob/03d6534e88ab8335aee2807e14aeecb80e118001/samples/uploadFileInChunksWithTransferManager.js#L28), tag `storage_transfer_manager_upload_chunks_concurrently`

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[generated-files-bot[bot]]

Warning: This pull request is touching the following templated files:

• README.md - README.md is managed by synthtool. However, a partials file can be used to update the README, e.g.: https://github.com/googleapis/nodejs-storage/blob/main/.readme-partials.yaml
• samples/README.md - samples/README.md is managed by synthtool. However, a partials file can be used to update the README, e.g.: https://github.com/googleapis/nodejs-storage/blob/main/.readme-partials.yaml

[ddelgrosso1]

Marking do not merge until we have final approval to go ahead with launch. Please review!