Add recipe: creating an extension that provides an AI engine

[GianTschingt]

New recipe docs/recipes/ai-engine-extension.md, explaining how an extension can provide its own AI engine, the same way the S3 extension provides a VFS resource provider.

• The lucee.runtime.ai.* interfaces in the loader (since 7.0.0.114, LDEV-5368), with their signatures, and what Lucee expects from an implementation
• A minimal engine and session for OpenAI compatible chat/completions endpoints, using only the JDK (java.net.http) and the loader API
• Packaging as a .lex, both as an OSGi bundle and as a Maven artifact (start-bundles: false)
• Registering the engine with an ai entry (class + bundleName/bundleVersion or maven, custom). There is no manifest key for AI engines.
• Using it from CFML, with links to the related recipes

The example code compiles (javac --release 11 -Xlint:all -Werror) against the 7.0.5.41, 7.1.1.15-RC and 8.0.0.189-SNAPSHOT loaders. It was tested as an installed extension (OSGi and Maven) on 7.1.1.15-RC and 8.0.0.189-SNAPSHOT against a local mock endpoint.

Index, README and lucee.skill regenerated with .github/scripts/generate-index-recipes.js.

Possible follow-ups (not changed here):

• loader-api-changes-7.md names AICreateSession and AIChat as functions. aiCreateSession exists as an alias, but there's no AIChat. The functions are createAISession()/inquiryAISession() (aliases aiCreateSession/aiInquirySession).
• extension-utilities.md lists the AI util as "Since: 6.2", but CFMLEngine.getAIUtil() only exists from 7.0. The example also doesn't match the interface: it is List<String> getModelNames(AIEngine) and getMetaData(AIEngine, boolean, boolean), not getModelNames(null) returning String[] or getAIMetadata(pc, name, false).
• ai.md mentions getAIMetadata()/LuceeGetAIMetadata(); the functions are AIGetMetaData()/LuceeAIGetMetaData().
• On 8.0.0.189-SNAPSHOT, createAISession(name:, systemMessage:) without limit/temperature passes limit=1 and temperature=1 to the engine (also with the core OpenAIEngine), so only the last exchange is kept in the history. 7.1 passes the FLD defaults 50/0.7. This looks related to the defaults being removed from the 8.0 FLD.