Rename appsource go module to github.com/argoproj-labs/appsource

The appsource module is currently named `github.com/argoproj-labs/argocd-app-source`, when the repo was migrated into argoproj-labs I changed the name of the repo to just `appsource`. With that change now Golang documentation site can't resolve the name `github.com/argoproj-labs/argocd-app-source`

# Proposal

Use [this](https://gist.github.com/iamucil/7578dc7df7d72e1d78c8f5543db3fbcc) rename module script to change the module name and replace all references to the import to the new module name `github.com/argoproj-labs/appsource`

Start by locating the Go module declaration and all references to github.com/argoproj-labs/argocd-app-source. Review the linked module rename script for the intended scope, then verify that imports use github.com/argoproj-labs/appsource and that the project still builds and tests successfully.

Written by the indexing model from the issue text.