[Feature Request] Allow tracing .NET processes from startup with dotnet-trace without the ability to set an environment variable

Currently to trace at startup we support two approaches for user experience:
1. The user launches the app by providing the command line to dotnet-trace (dotnet-trace collect -- foo.exe arg1 arg2)
2. The user set DOTNET_DiagnosticPorts=xyz and uses dotnet-trace --diagnostic-port xyz to listen once the process is eventually launched

In a separate issue it was hypothesized that we'd get scenarios where the user isn't sufficiently in control of the process being launched to set environment variables. I don't think we have a concrete example of what that is just yet but we can use this issue for further discussion to clarify what the need is. The discussion first arose in https://github.com/dotnet/diagnostics/issues/1946#issuecomment-771314705