Process $DB_INITIALIZE and $DB_MIGRATE variables

if $DB_INITIALIZE is present, deploy an initial release
where only $DB_INITIALIZE is run in a special job (and deployments are
not rendered/loaded). This is then followed by second release with
deployments as usual.

if $DB_MIGRATE, set this value which will trigger a pre-upgrade helm
hook.

changelogs/unreleased/48004-db-initialize-migrate.yml

+---
+title: Support db migration and initialization for Auto DevOps
+merge_request: 21955
+author:
+type: added

lib/gitlab/ci/templates/Auto-DevOps.gitlab-ci.yml

@@ -587,6 +587,7 @@ rollout 100%:
       secret_name=''
     fi
 
+    if [[ -n "$DB_INITIALIZE" && -z "$(helm ls -q "^$name$")" ]]; then
       helm upgrade --install \
         --wait \
         --set service.enabled="$service_enabled" \
@@ -604,10 +605,42 @@ rollout 100%:
         --set postgresql.postgresUser="$POSTGRES_USER" \
         --set postgresql.postgresPassword="$POSTGRES_PASSWORD" \
         --set postgresql.postgresDatabase="$POSTGRES_DB" \
+        --set application.initializeCommand="$DB_INITIALIZE" \
         --namespace="$KUBE_NAMESPACE" \
         "$name" \
         chart/
 
+      helm upgrade --reuse-values \
+        --wait \
+        --set application.initializeCommand="" \
+        --set application.migrateCommand="$DB_MIGRATE" \
+        --namespace="$KUBE_NAMESPACE" \
+        "$name" \
+        chart/
+    else
+      helm upgrade --install \
+        --wait \
+        --set service.enabled="$service_enabled" \
+        --set releaseOverride="$CI_ENVIRONMENT_SLUG" \
+        --set image.repository="$CI_APPLICATION_REPOSITORY" \
+        --set image.tag="$CI_APPLICATION_TAG" \
+        --set image.pullPolicy=IfNotPresent \
+        --set image.secrets[0].name="$secret_name" \
+        --set application.track="$track" \
+        --set application.database_url="$DATABASE_URL" \
+        --set service.url="$CI_ENVIRONMENT_URL" \
+        --set replicaCount="$replicas" \
+        --set postgresql.enabled="$postgres_enabled" \
+        --set postgresql.nameOverride="postgres" \
+        --set postgresql.postgresUser="$POSTGRES_USER" \
+        --set postgresql.postgresPassword="$POSTGRES_PASSWORD" \
+        --set postgresql.postgresDatabase="$POSTGRES_DB" \
+        --set application.migrateCommand="$DB_MIGRATE" \
+        --namespace="$KUBE_NAMESPACE" \
+        "$name" \
+        chart/
+    fi
+
     kubectl rollout status -n "$KUBE_NAMESPACE" -w "deployment/$name"
   }