Update new app template to reflect flux2

.gitlab/issue_templates/new_app.md

-# Template for integrating a new app
+# Integrate new app
 
-## Single sign-on
 
-* [ ] Integrate the new app into the signle sign-on system
-* [ ] Make sure the application does not allow registering through the
-  traditional sign-on system
-
-## Documentation
+## Flux
 
-* [ ] Add app to `docs/installation_instructions.md`
-* [ ] Add app to `docs/testing_instructions.md`
+* [ ] Create new source if needed in `flux2/infrastructure/sources/APP.yaml`
+* [ ] Include `APP.yaml` in `flux2/infrastructure/sources/kustomization.yaml`
+* [ ] Add app secret: `charts/oas-secrets/templates/oas-APP-variables.yaml`
+* Add kustomisations:
+   * [ ] `flux2/cluster/optional/wekan/APP.yaml`
+   * [ ] `flux2/apps/APP/kustomization.yaml`
+   * [ ] Add pvc in `flux2/apps/APP/pvc.yaml`
+   * [ ] Add helmrelease in `flux2/apps/APP/release.yaml`
 
-## Etc
+### Single sign-on
 
-* [ ] Make sure to use an `existingClaim` for persistent volumes
+* Integrate the new app into the single sign-on system
+  * Add OAuth client secret to `charts/oas-secrets/templates/oas-oauth-variables.yaml`
+  * In `flux2/core/base/single-sign-on/release.yaml`:
+    * [ ] Add app `userbackend.applications`
+    * [ ] Add app to `oAuthClients`
+  * Confgure app OIDC settings in helmrelease `flux2/apps/APP/release.yaml`
+* [ ] Make sure the application does not allow registering through the
+  traditional sign-on system
 
 ## Tests
 
-* [ ] Add taiko test (`tests/taiko`)
-* [ ] Check for successful helmrelease (`test/pytest/test_helmreleases.py`)
 * [ ] Test cert (`test/pytest/test_certs.py`)
+* [ ] Add taiko test (`tests/taiko`)
 
 ## CI
 
-* [ ] Run new tests in CI (`.gitlab-ci.yml`)
+Add app to following stages in `.gitlab-ci.yml`:
+
+* [ ] install-apps
+* [ ] apps-helm-release
+* [ ] apps-ready
+* [ ] certs
+* [ ] integration-tests
+
+## Documentation
+
+* Add app to:
+  * [ ] `docs/installation_instructions.rst`
+  * [ ] `docs/testing_instructions.rst`
+  * [ ] `docs/usage.rst`