Merge branch 'microsoft-teams-integration' into 'master'

app/models/project.rb

app/models/project_services/chat_message/base_message.rb

app/models/project_services/chat_message/issue_message.rb

app/models/project_services/chat_message/merge_message.rb

app/models/project_services/chat_message/note_message.rb

app/models/project_services/chat_message/pipeline_message.rb

app/models/project_services/chat_message/push_message.rb

...models/project_services/chat_message/wiki_page_message.rb

app/models/project_services/chat_notification_service.rb

app/models/project_services/microsoft_teams_service.rb

app/models/service.rb

changelogs/unreleased/microsoft-teams-integration.yml

...roject/integrations/img/microsoft_teams_configuration.png

doc/user/project/integrations/microsoft_teams.md

lib/api/services.rb

lib/api/v3/services.rb

lib/microsoft_teams/activity.rb

lib/microsoft_teams/notifier.rb

spec/lib/gitlab/import_export/all_models.yml

spec/lib/microsoft_teams/activity_spec.rb