Fix module name for GMP, update docs, and prepare for a patch release.

[dashpole]

It isn't currently possible to use the GMP exporter because of the module name:

Error: failed to update go.mod: exit status 1. Output: "go: downloading github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/collector/googlemanagedprometheus v0.30.0\ngo: github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/collector/googlemanagedprometheus@v0.30.0: parsing go.mod:\n\tmodule declares its path as: github.com/dashpole/opentelemetry-operations-go/exporter/collector/googlemanagedprometheus\n\t        but was required as: github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/collector/googlemanagedprometheus\n"

I had changed it to dashpole while I was manually testing, but forgot to change it back.