Json schema for vendir spec

**Describe the problem/challenge you have**

It would be convenient to have coding assistance from IDE when reading/editing a vendir.yaml file

**Describe the solution you'd like**

Formatting the https://carvel.dev/vendir/docs/v0.34.x/vendir-spec/ as a https://json-schema.org/ and registering it into https://www.schemastore.org/json/ would automatically enable most recent IDEs (e.g. intellij, vscode) to automatically provide:
- inline doc
- completion
- static analysis

**Anything else you would like to add:**
[Additional information that will assist in solving the issue.]

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