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

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

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

@@ -2,9 +2,10 @@
 set -e -u -o pipefail
 cd "$(dirname "$0")"
 . .e2erc
+[ -f .env.cloud ] && . .env.cloud
 
-if [ "$SERVER" != "cloud" ]; then
-  mme2e_log "Skipping cloud instance teardown: operation supported only for cloud server, but running with SERVER='$SERVER'"
+if [ -z "${MM_CUSTOMER_ID:-}" ]; then
+  mme2e_log "Skipping cloud instance teardown: MM_CUSTOMER_ID variable is empty, no cloud user to cleanup."
   exit 0
 fi
 
@@ -20,5 +21,6 @@ MME2E_ENVCHECK_MSG="variable required for tearing down cloud tests, but is empty
 
 mme2e_log "Deleting customer $MM_CUSTOMER_ID."
 curl -fsSL -X DELETE -H @- "${CWS_URL}/api/v1/tests/customers/$MM_CUSTOMER_ID/payment-customer" <<<"${CWS_EXTRA_HTTP_HEADERS:-}"
+rm -fv .env.cloud
 
 mme2e_log "Test cloud customer deleted, MM_CUSTOMER_ID: $MM_CUSTOMER_ID."