Add Prevent Sharing Groups Column to Namespace Settings Table

What does this MR do?

Add prevent_sharing_groups_outside_hierarchy column to the namespace_settings table.

When true, groups can be shared only with other groups that lie within the group hierarchy.

The proof of concept for this issue shows how this fits into the overall picture with the rest of the code to implement the feature: !62623 (closed). In the proof of concept, this column was called share_within_hierarchy_lock.

Issue: #217623 (closed)

Migration Output

$ bin/rails db:migrate
== 20210527185542 AddPreventSharingGroupsOutsideHierarchyToNamespaceSettings: migrating 
-- add_column(:namespace_settings, :prevent_sharing_groups_outside_hierarchy, :boolean, {:null=>false, :default=>false})
   -> 0.0022s
== 20210527185542 AddPreventSharingGroupsOutsideHierarchyToNamespaceSettings: migrated (0.0087s) 

$ bin/rails dbconsole
psql (12.7)
Type "help" for help.

gitlabhq_development=# \d namespace_settings
                                  Table "public.namespace_settings"
                  Column                  |           Type           | Collation | Nullable | Default 
------------------------------------------+--------------------------+-----------+----------+---------
 created_at                               | timestamp with time zone |           | not null | 
 updated_at                               | timestamp with time zone |           | not null | 
 namespace_id                             | integer                  |           | not null | 
 prevent_forking_outside_group            | boolean                  |           | not null | false
 allow_mfa_for_subgroups                  | boolean                  |           | not null | true
 default_branch_name                      | text                     |           |          | 
 repository_read_only                     | boolean                  |           | not null | false
 delayed_project_removal                  | boolean                  |           |          | 
 resource_access_token_creation_allowed   | boolean                  |           | not null | true
 lock_delayed_project_removal             | boolean                  |           | not null | false
 prevent_sharing_groups_outside_hierarchy | boolean                  |           | not null | false
Indexes:
    "namespace_settings_pkey" PRIMARY KEY, btree (namespace_id)
Check constraints:
    "check_0ba93c78c7" CHECK (char_length(default_branch_name) <= 255)
Foreign-key constraints:
    "fk_rails_3896d4fae5" FOREIGN KEY (namespace_id) REFERENCES namespaces(id) ON DELETE CASCADE

gitlabhq_development=# \q
$ bin/rails db:rollback
== 20210527185542 AddPreventSharingGroupsOutsideHierarchyToNamespaceSettings: reverting 
-- remove_column(:namespace_settings, :prevent_sharing_groups_outside_hierarchy)
   -> 0.0014s
== 20210527185542 AddPreventSharingGroupsOutsideHierarchyToNamespaceSettings: reverted (0.0084s) 

$ bin/rails dbconsole  
psql (12.7)
Type "help" for help.

gitlabhq_development=# \d namespace_settings
                                 Table "public.namespace_settings"
                 Column                 |           Type           | Collation | Nullable | Default 
----------------------------------------+--------------------------+-----------+----------+---------
 created_at                             | timestamp with time zone |           | not null | 
 updated_at                             | timestamp with time zone |           | not null | 
 namespace_id                           | integer                  |           | not null | 
 prevent_forking_outside_group          | boolean                  |           | not null | false
 allow_mfa_for_subgroups                | boolean                  |           | not null | true
 default_branch_name                    | text                     |           |          | 
 repository_read_only                   | boolean                  |           | not null | false
 delayed_project_removal                | boolean                  |           |          | 
 resource_access_token_creation_allowed | boolean                  |           | not null | true
 lock_delayed_project_removal           | boolean                  |           | not null | false
Indexes:
    "namespace_settings_pkey" PRIMARY KEY, btree (namespace_id)
Check constraints:
    "check_0ba93c78c7" CHECK (char_length(default_branch_name) <= 255)
Foreign-key constraints:
    "fk_rails_3896d4fae5" FOREIGN KEY (namespace_id) REFERENCES namespaces(id) ON DELETE CASCADE

gitlabhq_development=# \q
$ 

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