feat: add support for browser streaming

[AllanZhengYP]

Reopen #581

Per #102 browser streaming as removed from preview because ReadableStream support in browsers was not ideal back then. Now since most of the browser vendors support ReadableStream, we can enable the feature.

Previously, the fetch-http-handler returns a promise of blob for body, even when we expect the body to be streaming sometimes(e.g. S3 GetObject). After these change, we can return a ReadableStream for streaming response in browser. This would avoid loading all the resposne body data in the brwoser memory.

reference:

• ReadableStream browser support: https://caniuse.com/#search=ReadableStream
• ReadableStream update for browser support data: Update ReadableStream compatibility in Safari mdn/browser-compat-data#5424
• Response constructor: https://fetch.spec.whatwg.org/#response-class
• Response constructor browser compatibility: https://caniuse.com/#feat=mdn-api_response_response
• spec for converting response to arrayBuffer: https://fetch.spec.whatwg.org/#body-mixin
• Body(e.g. Body.arraybuffer()) update for browser support data: add body api safari, safari mobile, chrome android support mdn/browser-compat-data#5490
• Body Body and Readable stream support data is not accurate. They are actually supported by
  current mainstream browsers, desktop and mobile. See above 2 PRs for more information.

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[AllanZhengYP]

This CI is failing because my update to streaming-collector-browser package requires karma test, running jest on it will fail with Response is not defined. Now we run run jest directly to the whole workspace. We need a path to run karma only for some sub-packages. One way to achieve it is to run lerna exec "yarn test" in CI so we can run test script to each package.

Update: This issue is mentioned in #671

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[AllanZhengYP]

After fixing the CodeBuild image, the CI finally succeeds. Now this is ready to be reviewed.

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