Create Operations User Lists Table

What does this MR do?

Add a migration to create the operations_user_lists table. This is the table for #205409 (closed), which is the CRUD API for user lists for use with feature flags.

Issue: #205409 (closed)

Migration Output

$  bin/rails db:migrate
== 20200401211005 CreateOperationsUserLists: migrating ========================
-- create_table(:operations_user_lists)
   -> 0.0110s
== 20200401211005 CreateOperationsUserLists: migrated (0.0110s) ===============

$ bin/rails dbconsole
psql (10.12)
Type "help" for help.

gitlabhq_development=# \d operations_user_lists
                                       Table "public.operations_user_lists"
   Column   |           Type           | Collation | Nullable |                      Default                      
------------+--------------------------+-----------+----------+---------------------------------------------------
 id         | bigint                   |           | not null | nextval('operations_user_lists_id_seq'::regclass)
 project_id | bigint                   |           | not null | 
 created_at | timestamp with time zone |           | not null | 
 updated_at | timestamp with time zone |           | not null | 
 iid        | integer                  |           | not null | 
 name       | character varying(255)   |           | not null | 
 user_ids   | text                     |           | not null | ''::text
Indexes:
    "operations_user_lists_pkey" PRIMARY KEY, btree (id)
    "index_operations_user_lists_on_project_id_and_iid" UNIQUE, btree (project_id, iid)
    "index_operations_user_lists_on_project_id_and_name" UNIQUE, btree (project_id, name)
Foreign-key constraints:
    "fk_rails_0c716e079b" FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE

gitlabhq_development=# \q
$ bin/rails db:rollback
== 20200401211005 CreateOperationsUserLists: reverting ========================
-- drop_table(:operations_user_lists)
   -> 0.0018s
== 20200401211005 CreateOperationsUserLists: reverted (0.0028s) ===============

$ 

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

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team