Move endpoint installation to the HostApplicationBuilder level

[DavidBoike]

Note

• Currently dependent upon Spike: Make endpoint identifier an optional string override of endpoint name #7687 and will need work after that PR is completed, either way.
• To review the code specific to this PR in the meantime, ignore the first 3 commits.

Instead of separate methods for registering endpoints vs. registering endpoint installers, instead this spike shows how installation could be a host-level concern, allowing usage like this:

var endpointConfiguration = new("EndpointName");
// configure endpoint

var builder = Host.CreateApplicationBuilder();
builder.Services.AddNServiceBusEndpoint(endpointConfiguration);

if (isInstall)
{
    await builder.InstallNServiceBusEndpoints();
}
else
{
    await builder.Build().Run();
}

InstallNServiceBusEndpoints() runs Create() on the endpoint, and then also forces installers to run, whether or not endpointConfiguration.EnableInstallers() was set, as the settings are finalized when the endpoints are added to the IServiceCollection. No user code or hosted services are run except what would need to be injected into NServiceBus component responsible for installing the endpoint.

The implementation calls builder.Build() and does not return the intermediate IHost so the builder cannot (by design) be used to also attempt to start the endpoints.

The result is much less need for testing that, for example, endpoints and installers aren't mixed, or registered as both endpoint and installer, etc.

Currently a little hacky, especially the extent to which forceRunInstallers is pushed through several levels, but I wanted to begin at a layer where the endpoint-specific keyed serviceProvider was already known.

[DavidBoike]

• Replaced by Add AddNServiceBusInstallers for Generic Host Integration #7709