docs(spec): note --spec-format removal as breaking change from APIOps Toolkit

Adds an explicit assumption in specs/spec.md noting that not carrying
forward the toolkit's API_SPECIFICATION_FORMAT / --spec-format option is
a known breaking change. apiops-cli extracts REST APIs as OpenAPI v3 YAML
only; users relying on v2 or JSON variants must migrate.

Addresses review feedback from @EMaher on PR #165.

Author: Peter Hauge

specs/spec.md

@@ -208,4 +208,5 @@ The development team wants the CLI to support adding new top-level commands (e.g
 - The tool is distributed as an npm package and/or standalone binary; distribution mechanism details are deferred to implementation planning.
 - APIM API secrets (named value values marked as secrets, subscription keys) are NOT extracted in plaintext — they must be handled via override configuration or key vault references.
 - GraphQL and SOAP/WSDL APIs are supported for extraction in their native formats; format conversion between these and OpenAPI is out of scope.
+- For REST APIs, specifications are extracted in OpenAPI v3 YAML only. The APIOps Toolkit's `API_SPECIFICATION_FORMAT` / `--spec-format` option (which allowed selecting `OpenAPIV2Json`, `OpenAPIV2Yaml`, `OpenAPIV3Json`, or `OpenAPIV3Yaml`) is intentionally not carried forward. This is a known breaking change from the APIOps Toolkit: users who relied on OpenAPI v2 output or JSON output will need to migrate to OpenAPI v3 YAML. SC-006 (toolkit artifact compatibility) covers directory layout, not spec format variants.
 - Instance-specific resources (authorization servers, OpenID Connect providers, certificates, caches, identity providers, portal configuration, content types/items, notifications, users, tenant settings) are intentionally excluded — they do not belong in environment-promotion pipelines.