[WIP] @loopback/boot handle ECMA scripts

[ecurien]

Checklist

• [x] DCO (Developer Certificate of Origin) signed in all commits
• [x] npm test passes on your machine
• [x] New tests added or existing tests modified to cover all changes
• [x] Code conforms with the style guide
• [x] API Documentation in code was updated
• [n/a] Documentation in /docs/site was updated
• [n/a] Affected artifact templates in packages/cli were updated
• [n/a] Affected example projects in examples/* were updated

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EDIT: Only one integration test is typeorm does not path. I really do not understand why. Could someone help with this ?