Added Copilot setup

[xperiandri]

No description provided.

[Copilot]

Pull Request Overview

This PR modernizes the project by migrating from traditional .sln files to the new .slnx format and adds Copilot integration setup. The change represents an adoption of Microsoft's XML-based solution format that offers better tooling integration and maintainability.

• Migrates all solution files from .sln to .slnx format across the project
• Adds Copilot setup configuration including workflow and instructions
• Updates package references and MIME type mappings to support new file formats

Reviewed Changes

Copilot reviewed 4 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/FSharp.Data.GraphQL.Client/MimeTypes.fs	Adds MIME type mappings for .slnf and .slnx file extensions
samples/star-wars-fabulous-client/StarWars.slnx	Creates new XML-based solution file replacing the traditional .sln format
samples/star-wars-fabulous-client/StarWars.sln	Removes the legacy .sln solution file
build/Program.fs	Updates build script to reference the new .slnx file format
Packages.props	Updates package version constraints for compatibility
FSharp.Data.GraphQL.slnx	Creates main solution file in new XML format
FSharp.Data.GraphQL.sln	Removes legacy main solution file
FSharp.Data.GraphQL.Integration.slnx	Creates integration solution in new format
FSharp.Data.GraphQL.Integration.sln	Removes legacy integration solution
FSharp.Data.GraphQL.Build.slnx	Creates build solution in new format
FSharp.Data.GraphQL.Build.sln	Removes legacy build solution
.mcp.json	Adds MCP configuration for Copilot integration
.github/workflows/copilot-setup-steps.yml	Adds GitHub workflow for Copilot setup automation
.github/copilot-instructions.md	Adds comprehensive Copilot instructions and coding standards

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