Feature: dingtalk integration foundation

JH issue link, https://jihulab.com/gitlab-cn/gitlab/-/issues/531 and https://jihulab.com/gitlab-cn/gitlab/-/issues/532
related discuss issue: #354069 (comment 887870878)
JH MR: https://jihulab.com/gitlab-cn/gitlab/-/merge_requests/417

app/views/admin/application_settings/general.html.haml

use for root admin to turn on/off dingtalk integration

db/docs/dingtalk_tracker_data.yml

dingtalk_tracker_data model is in jihu repo. but need add this yml file to pass doc_spec.rb, not sure this is acceptable.
rspec ./spec/db/docs_spec.rb:51 # Database Documentation for each table has a metadata file

lib/gitlab/database/gitlab_schemas.yml

add dingtalk_tracker_data model which introduce new table, need add this table to pass db schema check, not sure this is acceptable

spec/lib/gitlab/import_export/all_models.yml

add model Integrations::Dingtalk and Integrations::DingtalkTrackerData, which breaks import/export spec, add this to make it pass, not sure this is acceptable
rspec ./spec/lib/gitlab/import_export/model_configuration_spec.rb:16 # Import/Export model configuration has no new models

cc: @daveliu