Closes #58

This pull request includes several changes to the Aspire.CommunityToolkit.sln solution and introduces a new project for Marten integration. The most important changes include updating project GUIDs, adding new package references, and implementing Marten client configuration and health checks.

Solution File Updates:

• Updated project GUIDs for multiple projects to ensure consistency in Aspire.CommunityToolkit.sln. [1] [2]
• Added the new Aspire.CommunityToolkit.Marten project to the solution. [1] [2]

Package References:

• Added AspNetCore.HealthChecks.NpgSql and Marten package references in Directory.Packages.props. [1] [2]

New Project for Marten Integration:

• Created Aspire.CommunityToolkit.Marten.csproj with necessary package references and file links.
• Implemented MartenApplicationBuilderExtensions to configure Marten clients and health checks.
• Added MartenSettings class to manage Marten client configuration settings.

Miscellaneous:

• Updated DocsPath in Directory.Build.props to point to README.md. [1] [2]
• Added HealthChecksExtensions to support conditional health check registration.

PR Checklist

• Based off latest main branch of toolkit
• New integration
  • Docs are written
  • Added description of major feature to project description for NuGet package (4000 total character limit, so don't push entire description over that)
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Contains NO breaking changes
• Every new API (including internal ones) has full XML docs
• Code follows all style conventions

one thing we should consider is NpgsqlDataSource registration should not make conflict with other NpgsqlDataSource instance. (for instance NpgsqlDataSource registration in Aspire.NpgSql)

builder.Services.AddKeyedSingleton<NpgsqlDataSource>(serviceKey is null ? "Aspire.Marten" : $"Aspire.Marten_{connectionName}", (serviceProvider, _) =>
        {
            ValidateConnectionString(settings.ConnectionString, connectionName, DefaultConfigSectionName);
            var dataSourceBuilder = new NpgsqlDataSourceBuilder(settings.ConnectionString);
            dataSourceBuilder.UseLoggerFactory(serviceProvider.GetService<ILoggerFactory>());
            return dataSourceBuilder.Build();
        });

Other information