Adds support for Matrix notification integration

.rubocop_todo/layout/line_length.yml

.rubocop_todo/rspec/named_subject.yml

app/models/integration.rb

app/models/integrations/matrix.rb

app/models/project.rb

..._all/20240722124654_projects_inheriting_matrix_active.yml

...etrics/counts_all/20240722124725_groups_matrix_active.yml

...rics/counts_all/20240722124754_projects_matrix_active.yml

...ts_all/20240722124827_groups_inheriting_matrix_active.yml

...ics/counts_all/20240722125029_instances_matrix_active.yml

db/docs/integrations.yml

doc/api/graphql/reference/index.md

doc/api/integrations.md

doc/user/project/integrations/index.md

doc/user/project/integrations/matrix.md

lib/api/helpers/integrations_helpers.rb

locale/gitlab.pot

spec/factories/integrations.rb

spec/lib/gitlab/import_export/all_models.yml

spec/models/integrations/matrix_spec.rb