Create requirements test reports table and model

What does this MR do?

Create model and table for requirement test reports.

Migration output

== 20200511181027 CreateTestReports: migrating ================================
-- create_table(:requirements_management_test_reports)
   -> 0.0215s
== 20200511181027 CreateTestReports: migrated (0.0215s) =======================

== 20200511191027 AddAuthorForeignKeyToTestReports: migrating =================
-- add_foreign_key(:requirements_management_test_reports, :users, {:column=>:author_id, :on_delete=>:nullify})
   -> 0.0027s
== 20200511191027 AddAuthorForeignKeyToTestReports: migrated (0.0088s) ========

== 20200511208012 AddPipelineForeignKeyToTestReports: migrating ===============
-- add_foreign_key(:requirements_management_test_reports, :ci_pipelines, {:column=>:pipeline_id, :on_delete=>:nullify})
   -> 0.0019s
== 20200511208012 AddPipelineForeignKeyToTestReports: migrated (0.0058s) ======

Related to #215506 (closed)