CLD-5783 Implement rolling upgrade tests (#27842)

* Make server.prepare idempotent, don't cleanup containers on server.start
* Implement rolling upgrade E2E tests
* Apply Akis' suggestions from code review
* Apply Saturn's suggestions from review
* Communicate RollingRelease on GHA and test automation results channel
* Implement E2E test case versioning for rolling release tests

---------

Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Akis Maziotis <akis.maziotis@mattermost.com>

e2e-tests/.ci/server.prepare.sh

@@ -26,16 +26,33 @@ if [ "$TEST" = "cypress" ]; then
   ${MME2E_DC_SERVER} exec -T -u "$MME2E_UID" -- cypress npm i
   ${MME2E_DC_SERVER} exec -T -u "$MME2E_UID" -- cypress cypress install
   mme2e_log "Prepare Cypress: populating fixtures"
-  ${MME2E_DC_SERVER} exec -T -- server curl -L --silent https://github.com/mattermost/mattermost-plugin-gitlab/releases/download/v1.3.0/com.github.manland.mattermost-plugin-gitlab-1.3.0.tar.gz | ${MME2E_DC_SERVER} exec -T -u "$MME2E_UID" -- cypress tee tests/fixtures/com.github.manland.mattermost-plugin-gitlab-1.3.0.tar.gz >/dev/null
-  ${MME2E_DC_SERVER} exec -T -- server curl -L --silent https://github.com/mattermost/mattermost-plugin-demo/releases/download/v0.9.0/com.mattermost.demo-plugin-0.9.0.tar.gz | ${MME2E_DC_SERVER} exec -T -u "$MME2E_UID" -- cypress tee tests/fixtures/com.mattermost.demo-plugin-0.9.0.tar.gz >/dev/null
-  ${MME2E_DC_SERVER} exec -T -- server curl -L --silent https://github.com/mattermost/mattermost-plugin-demo/releases/download/v0.8.0/com.mattermost.demo-plugin-0.8.0.tar.gz | ${MME2E_DC_SERVER} exec -T -u "$MME2E_UID" -- cypress tee tests/fixtures/com.mattermost.demo-plugin-0.8.0.tar.gz >/dev/null
   ${MME2E_DC_SERVER} exec -T -u "$MME2E_UID" -- cypress tee tests/fixtures/keycloak.crt >/dev/null <../../server/build/docker/keycloak/keycloak.crt
+  for PLUGIN_URL in \
+    "https://github.com/mattermost/mattermost-plugin-gitlab/releases/download/v1.3.0/com.github.manland.mattermost-plugin-gitlab-1.3.0.tar.gz" \
+    "https://github.com/mattermost/mattermost-plugin-demo/releases/download/v0.9.0/com.mattermost.demo-plugin-0.9.0.tar.gz" \
+    "https://github.com/mattermost/mattermost-plugin-demo/releases/download/v0.8.0/com.mattermost.demo-plugin-0.8.0.tar.gz"
+  do
+    PLUGIN_NAME="${PLUGIN_URL##*/}"
+    PLUGIN_PATH="tests/fixtures/$PLUGIN_NAME"
+    if ${MME2E_DC_SERVER} exec -T -u "$MME2E_UID" -- cypress test -f "$PLUGIN_PATH"; then
+      mme2e_log "Skipping installation of plugin $PLUGIN_NAME: file exists"
+      continue
+    fi
+    mme2e_log "Downloading $PLUGIN_NAME to fixtures directory"
+    ${MME2E_DC_SERVER} exec -T -- server curl -L --silent "${PLUGIN_URL}" | ${MME2E_DC_SERVER} exec -T -u "$MME2E_UID" -- cypress tee "$PLUGIN_PATH" >/dev/null
+  done
 fi
 
 # Run service-specific initialization steps
 for SERVICE in $ENABLED_DOCKER_SERVICES; do
   case "$SERVICE" in
   openldap)
+    LDIF_FILE=../../server/tests/test-data.ldif
+    LDIF_CANARY=$(sed -n -E 's/^dn:[[:space:]]*(.*)$/\1/p' ${LDIF_FILE} | tail -n1)
+    if ${MME2E_DC_SERVER} exec -T -- openldap bash -c "ldapsearch -x -D \"cn=admin,dc=mm,dc=test,dc=com\" -w mostest -b \"$LDIF_CANARY\" >/dev/null"; then
+      mme2e_log "Skipping configuration for the $SERVICE container: already initialized"
+      continue
+    fi
     mme2e_log "Configuring the $SERVICE container"
     ${MME2E_DC_SERVER} exec -T -- openldap bash -c 'ldapadd -x -D "cn=admin,dc=mm,dc=test,dc=com" -w mostest' <../../server/tests/test-data.ldif
     ;;