Fix SQL N+1 problem in Packages::Go::RefreshPackagesService

In working on !29642 (closed), I have introduced a SQL N+1 problem. I am creating this issue in order to whitelist the API so I can run tests and verify that the logic is valid.

Packages::Go::RefreshPackagesService scans a repository for semver tags containing go.mod files, and creates a Packages::Package for each (path, tag) pair. These packages may also have Packages::PackageFile entries. To avoid duplicating existing records, Packages::Go::CreatePackageService queries the database to check for existing records. This creates an N+1 SQL problem. The solution should be to preload records to limit the number of SQL queries, but my attempts have failed. From this discussion !29642 (comment 348692838):

The above means RefreshPackagesService has a serious N+1 SQL query problem, querying project.packages and package.project_files. I tested a variety of ideas, but nothing reliably prevented CreatePackageService from making tons of queries. You can see here that I tried creating a Project scope. I did some tests in the rails console, and it seems like where queries (e.g. Package#with_file_name) skip the preloaded results. I don't have much experience with Rails or ActiveRecord, so I would appreciate suggestions.

• Pipeline with failures
• Pipeline with queries logged
• Packages::Go::RefreshPackagesService
• Packages::Go::CreatePackageService