OTLP configuration is still injected into resources when the dashboard is disabled

When starting an AppHost project with the dashboard disabled, e.g. from a test using `DistributedApplicationTestBuilder.Create()`, the configuration for the dashboard's OTLP endpoint is still injected into the environment variables of resources, including projects and Node.js apps. Some resources may not handle being configured to egress OTLP to a non-existent endpoint as well as others so we should be sure not to configure resources for OTLP if we know the OTLP endpoint will not be started.