Rename language `spy-name` to something more intuitive and less abstract

When pyroscope was started it started with rbspy, py-spy and php-spy. As a result when we refer to the source languages for each of our profilers we refer to them as `spy-name`.

So if you are using:
- go you have to set `spy-name: gospy`
- python we automatically set `spy-name: py-spy`

etc

Now that we are re-thinking some of our labels and configuration options leading up to Pyroscope 1.0 release it seems like a good time to come up with a more solid foundation to build on moving forward post Pyroscope 1.0.

We should do two things:
1. rename `spy-name` field that accompanies all of our integrations to something more intuitive like `source`
2. we should ensure that this field is always either present or derived from somewhere when profiles are sent to the server

Similar to https://github.com/grafana/pyroscope/issues/2055