ApiDefinitionGuidelines: Add api-definitions-guidelines doc

Signed-off-by: Gabe Goodhart <[email protected]>

docs/api-definitions-guidelines.md

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+# API Definitions Guidelines
+
+This document describes how service APIs will be managed for `InstructLab` and the sub-components of the `InstructLab` backend.
+
+## What parts of InstructLab need service APIs?
+
+There are two primary classes of service APIs needed to support InstructLab:
+
+* `Platform APIs`: These are APIs that are ignorant of `InstructLab` and provide generic AI platform capabilities (e.g., Fine Tuning, SDG, Eval)
+* `InstructLab APIs`: These are the APIs that reflect the user-facing functionality of `InstructLab` itself. They are aware of the end-to-end `InstructLab` workflow.
+
+The `InstructLab APIs` are essential for hosting `InstructLab` as a service in a repeatable way. The `Platform APIs` are critical for component reuse and extensibility (e.g., new SDG algorithms for new taxonomy data types), but they are not strictly required for hosting `InstructLab` as a service.
+
+## How will service APIs be defined?
+
+Service APIs will be defined using [OpenAPI](https://www.openapis.org/) format in [yaml](https://yaml.org/). For structural and style guidelines, see [api-definitions](../api-definitions/README.md).
+
+## Where will service API definitions live?
+
+Service API definitions will live in [api-definitions](../api-definitions) within this repo.