Rewrite Get Started for the Collector and separate install instructions

[theletterf]

This solves #1695 and potentially a few others.

I went for the simplest possible approach:

• Download the binary or Docker image
• Run with default configuration
• Install telemetrygen
• Send traces
• Check in zpages

At the same time I've split the install instructions into a separate page.

The problem I'm seeing with using telemetrygen is that the official install instructions don't work (open-telemetry/opentelemetry-collector-contrib#27855) and that we don't provide a binary (open-telemetry/opentelemetry-collector-contrib#27856). I think the first issue should be solved, at least.

Note: I'm getting some errors in a blog post that I haven't touched...

[theletterf]

@mx-psi How could I replace the telemetrygen instructions so that they'd work? Getting rid of the Go dependency for the get started would be nice, but I guess that doing it all in docker would require creating a docker network first?

[mx-psi]

@mx-psi How could I replace the telemetrygen instructions so that they'd work? Getting rid of the Go dependency for the get started would be nice, but I guess that doing it all in docker would require creating a docker network first?

I think we should address open-telemetry/opentelemetry-collector-contrib#27855 and fix the go install

[svrnm]

make sure that your PR does not contain updates to the content-modules.

[svrnm]

Thanks for taking the time to write this down @theletterf! Some change requests and suggestions

[theletterf]

Closing this and opening #3426 due to pesky submodule issues...