Prefer `type: :task` over defining :environment task in rake specs

Problem

To test rake tasks we tend to require 'rake_helper' which includes RakeHelpers and sets up hooks related to type: :task. However, this extra file is not needed and the same functionality can be achieved when using require 'spec_helper'.

Proposed solution

• Remove use of require 'rake_helper' and use type: :task instead
• Include RakeHelpers only for type: :task via config.include RakeHelpers type: :task
• Replace instances of Rake::Task.define_task :environment with type: :task

Prior discussion

The following discussion from !131257 (merged) should be addressed:

• @engwan started a discussion: (+1 comment)

  Had to add this to fix https://gitlab.com/gitlab-org/gitlab/-/jobs/5074766630

@splattael wrote in !131257 (comment 1556790880):

I see that other instances define an environment task instead:

Rake::Task.define_task :environment

Perhaps using type: :task metatag is more obvious then? 🤔

The list of users of Rake.application outside of spec/tasks:

• spec/commands/metrics_server/metrics_server_spec.rb
• spec/lib/backup/database_spec.rb
• spec/lib/backup/manager_spec.rb
• spec/migrations/add_namespaces_emails_enabled_column_data_spec.rb
• spec/migrations/add_projects_emails_enabled_column_data_spec.rb
• spec/requests/api/usage_data_queries_spec.rb
• spec/support/helpers/rake_helpers.rb

We could follow-up on that though.