feat: add lb4 filter specifications draft

[achrinza]

Update 25 April 2022: One of the problems with the current approach of this work is that it pivots around a default JSON serialisation. This makes it difficult to perform information modelling and exposes the specification to the quirks of JSON. Since this work started, JSON Abstract Data Notation Committee Specification 01 (JADN CS01) was released. This specification allows for first-class information modelling with a built-in JSON, XML and CBOR serialisation strategy; This means that there's a clear path to converting from JADN to JSON Schema for compatibility with the current implementation in LoopBack 4. The plan is to rewrite the existing work to leverage JADN and publish JADN packages as normative references.

Signed-off-by: Rifa Achrinza [email protected]

Checklist

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

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