feature: Option to disable built-in / `cli` branch commands

[Kiruyuto]

Is your feature request related to a problem? Please describe.

I've built simple CLI app that I tried publishing with assembly trimming enabled and even though my application does not use the built-in Spectre CLI commands, they are still registered internally by, I believe, this part

spectre.console.cli/src/Spectre.Console.Cli/CommandApp.cs

Lines 64 to 72 in efdcbd5

	// Add built-in (hidden) commands.
	_configurator.AddBranch(CliConstants.Commands.Branch, cli =>
	{
	cli.HideBranch();
	cli.AddCommand<VersionCommand>(CliConstants.Commands.Version);
	cli.AddCommand<XmlDocCommand>(CliConstants.Commands.XmlDoc);
	cli.AddCommand<ExplainCommand>(CliConstants.Commands.Explain);
	cli.AddCommand<OpenCliGeneratorCommand>(CliConstants.Commands.OpenCli);
	});

In a trimmed publish, this causes runtime failures when invoking commands:

# in .csproj:
#    <PublishTrimmed>true</PublishTrimmed>
#    <TrimMode>full</TrimMode>
dotnet publish myApp -c Release -r win-x64 -p:SelfContained=true -p:PublishSingleFile=true -o artifacts/

# Custom command
./myApp.exe myCommand
Error: Could not get settings type for command of type 'Spectre.Console.Cli.VersionCommand'.

# Built-in
./myApp.exe cli version
Error: Could not get settings type for command of type 'Spectre.Console.Cli.VersionCommand'.

Also, since the VersionCommand is internal I cannot add dynamic dependency to my code

[DynamicDependency(DynamicallyAccessedMemberTypes.All, typeof(VersionCommand))] // <== Cannot access internal class 'VersionCommand' here

Describe the solution you'd like

My preferred option would be to disable built-in commands entirely, since Im not planning to use them.
This could be done for example during app configuration via

config.Settings.EnableBuiltInCommands = false;
// Or
config.DisableBuiltInCommands();

Alternatively, make those types public so they could be referenced

Describe alternatives you've considered

I used overload of DynamicDependency to preserve the built-in command to get around trimming failures, but it quickly gets messy. Also, as mentioned before it keeps commands that I do not need or really want to ship

Additional context

No additional context but if the maintainers consider this feature useful, Im happy to work on it
From a quick look, it seems like a relatively simple change