Add Golang Package type

What does this MR do?

Adds Go(lang) as a package type to Packages::Package and makes all the corresponding changes. Currently, Go packages are excluded from the API and UI. See #213770 (closed) and !34558 (merged).

DB Migration

Up

$ rails db:migrate:up RAILS_ENV=development VERSION=20200905013247
== 20200905013247 AddGolangPackageMaxFileSizeToPlanLimits: migrating ==========
-- add_column(:plan_limits, :golang_max_file_size, :bigint, {:default=>52428800, :null=>false})
   -> 0.0027s
== 20200905013247 AddGolangPackageMaxFileSizeToPlanLimits: migrated (0.0029s) =

Down

$ rails db:migrate:down RAILS_ENV=development VERSION=20200905013247
== 20200905013247 AddGolangPackageMaxFileSizeToPlanLimits: reverting ==========
-- remove_column(:plan_limits, :golang_max_file_size, :bigint, {:default=>52428800, :null=>false})
   -> 0.0033s
== 20200905013247 AddGolangPackageMaxFileSizeToPlanLimits: reverted (0.0060s) =

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done