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.start.sh

@@ -3,10 +3,6 @@ set -e -u -o pipefail
 cd "$(dirname "$0")"
 . .e2erc
 
-# Cleanup old containers, if any
-mme2e_log "Stopping leftover E2E containers, if any are running"
-${MME2E_DC_SERVER} down -v --remove-orphans
-
 # Wait for the required server image
 mme2e_log "Waiting for server image to be available"
 mme2e_wait_image "$SERVER_IMAGE" 4 30