Move allow developers to create projects in groups to Core

What does this MR do?

https://gitlab.com/gitlab-org/gitlab-ce/issues/44959

Move allow developers to create projects in groups to Core

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10057

Database checklist

• Conforms to the database guides

When adding migrations:

• Updated db/schema.rb
• Added a down method so the migration can be reverted
• Added the output of the migration(s) to the MR body
• Added tests for the migration in spec/migrations if necessary (e.g. when migrating data)

When adding or modifying queries to improve performance:

• Included data that shows the performance improvement, preferably in the form of a benchmark
• Included the output of EXPLAIN (ANALYZE, BUFFERS) of the relevant queries

When adding foreign keys to existing tables:

• Included a migration to remove orphaned rows in the source table before adding the foreign key
• Removed any instances of dependent: ... that may no longer be necessary

When adding tables:

• Ordered columns based on the Ordering Table Columns guidelines
• Added foreign keys to any columns pointing to data in other tables
• Added indexes for fields that are used in statements such as WHERE, ORDER BY, GROUP BY, and JOINs

When removing columns, tables, indexes or other structures:

• Removed these in a post-deployment migration
• Made sure the application no longer uses (or ignores) these structures

General checklist

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides

Migration output

== 20190311132500 AddDefaultProjectCreationSetting: migrating =================
-- column_exists?(:application_settings, :default_project_creation)
   -> 0.0108s
-- transaction_open?()
   -> 0.0000s
-- execute("SET statement_timeout TO 0")
   -> 0.0109s
-- transaction()
-- add_column(:application_settings, :default_project_creation, :integer, {:default=>nil})
   -> 0.0016s
-- change_column_default(:application_settings, :default_project_creation, 2)
   -> 0.0090s
   -> 0.0119s
-- transaction_open?()
   -> 0.0000s
-- exec_query("SELECT COUNT(*) AS count FROM \"application_settings\"")
   -> 0.0010s
-- exec_query("SELECT  \"application_settings\".\"id\" FROM \"application_settings\" ORDER BY \"application_settings\".\"id\" ASC LIMIT 1")
   -> 0.0020s
-- exec_query("SELECT  \"application_settings\".\"id\" FROM \"application_settings\" WHERE \"application_settings\".\"id\" >= 1 ORDER BY \"application_settings\".\"id\" ASC LIMIT 1 OFFSET 1")
   -> 0.0006s
-- execute("UPDATE \"application_settings\" SET \"default_project_creation\" = 2 WHERE \"application_settings\".\"id\" >= 1")
   -> 0.0009s
-- change_column_null(:application_settings, :default_project_creation, false)
   -> 0.0013s
-- execute("RESET ALL")
   -> 0.0003s
== 20190311132500 AddDefaultProjectCreationSetting: migrated (0.0490s) ========

== 20190311132527 AddProjectCreationLevelToNamespaces: migrating ==============
-- column_exists?(:namespaces, :project_creation_level)
   -> 0.0017s
-- add_column(:namespaces, :project_creation_level, :integer)
   -> 0.0006s
== 20190311132527 AddProjectCreationLevelToNamespaces: migrated (0.0023s) =====