CI updates to trigger a tpo/web/community build (#1)

Change GitLab CI/CD configuration to allow deployment under community.torproject.org/onion-services/ecosystem.

.gitlab-ci.yml

 ---
+variables:
+  GIT_SUBMODULE_STRATEGY: recursive
+
 include:
-  - local: '.gitlab-ci-pages.yml'
+  project: tpo/tpa/ci-templates
+  file:
+    - scripts/apt.yml
+    - pages-deploy.yml
+
+build:
+  image: debian:bookworm
+  stage: build
+  script:
+    - !reference [.apt-init]
+    - apt-get install -y git
+    - vendors/onion-mkdocs/scripts/onion-mkdocs-provision-build
+    - scripts/compile
+    - vendors/onion-mkdocs/scripts/onion-mkdocs-build
+  artifacts:
+    paths:
+      - public
+
+pages:
+  rules:
+    # canonical project: deploy to pages for main branch only
+    - if: '$CI_PROJECT_ROOT_NAMESPACE == "tpo" && $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH'
+    # forks: if merge request, deploy to pages on all branches
+    - if: '$CI_PROJECT_ROOT_NAMESPACE != "tpo" && $CI_PIPELINE_SOURCE == "merge_request"'
+
+# trigger a pipeline in tpo/web/community
+# to integrate and deploy latest builds
+trigger-community-build:
+  stage: deploy
+  needs:
+    - build
+  trigger:
+    project: tpo/web/community
+    branch: main
+  rules:
+    - if: '$CI_PROJECT_ROOT_NAMESPACE == "tpo" && $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH'