Layer for web-API deployment (OpenAPI support)

This is a placeholder, to describe the plan for OpenAPI support, which will be our primary vehicle to connect IFEX to HTTP-APIs.

- Just to remember that the associated layer should be able to define a data type by referring to a JSON schema, since it is ubiquitous in the web world to use schemas to constrain "values" that are passed as JSON documents.

The issue names no implementation files, tests, or entry points. Start by locating the IFEX layer definitions and existing format-processing paths, then review how OpenAPI and JSON Schema should connect HTTP APIs to IFEX. Done means an agreed, implementable layer design rather than a placeholder.

Written by the indexing model from the issue text.