Add basic support for agent runtime

[sebsto]

Add Amazon Bedrock Knowledge Base Retrieval Support

This PR adds support for Amazon Bedrock Agent Runtime's knowledge base retrieval functionality, enabling RAG (Retrieval-Augmented Generation) applications.

Key Changes:

• Added BedrockAgentRuntimeProtocol and client integration following existing patterns
• Added retrieve() function to BedrockService for querying knowledge bases
• Created RetrieveResult wrapper with convenience methods (bestMatch(), toJSON())
• Added comprehensive documentation and example application
• Updated Package.swift with AWSBedrockAgentRuntime dependency

Usage:

let result = try await bedrock.retrieve(
    knowledgeBaseId: "your-kb-id", 
    retrievalQuery: "your query"
)
let bestMatch = result.bestMatch()
let jsonContext = try result.toJSON() // For LLM context

[Copilot]

Pull Request Overview

This PR adds support for Amazon Bedrock Agent Runtime's knowledge base retrieval functionality, enabling Retrieval-Augmented Generation (RAG) applications in the Swift Bedrock Library.

Key Changes:

• Added BedrockAgentRuntimeProtocol and client integration following the existing pattern for other Bedrock clients
• Implemented retrieve() function in BedrockService for querying knowledge bases with configurable result counts
• Created RetrieveResult wrapper with convenience methods for accessing results and exporting to JSON

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Sources/BedrockService/BedrockService.swift	Integrated BedrockAgentRuntimeClient into BedrockService initialization
Sources/BedrockService/BedrockService+AgentRuntime.swift	Added client factory and retrieve() function for knowledge base queries
Sources/BedrockService/RetrieveResult.swift	Created result wrapper with bestMatch() and toJSON() convenience methods
Sources/BedrockService/Protocols/BedrockAgentRuntimeProtocol.swift	Added protocol for BedrockAgentRuntimeClient to enable mocking
Sources/BedrockService/Protocols/BedrockConfigProtocol.swift	Extended BedrockConfigProtocol conformance to BedrockAgentRuntimeClient
Sources/BedrockService/Docs.docc/Retrieval.md	Added comprehensive documentation with usage examples
Sources/BedrockService/Docs.docc/BedrockService.md	Added Retrieval documentation reference
Package.swift	Added AWSBedrockAgentRuntime dependency
Examples/retrieve/Sources/Retrieve.swift	Created example application demonstrating knowledge base retrieval
Examples/retrieve/Package.swift	Added package manifest for retrieve example
Examples/retrieve/.gitignore	Added gitignore for example project

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