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/Makefile

@@ -2,11 +2,11 @@ SHELL := /bin/bash
 
 .PHONY: all run stop clean
 all: run
-run: cloud-init generate-server start-server prepare-server run-test cloud-teardown
+run: generate-server start-server prepare-server run-test
 stop: stop-server stop-dashboard clean
 clean:
 	rm -fv .ci/server.yml
-	rm -fv .ci/.env*
+	rm -fv .ci/.env.{server,dashboard,cypress,playwright}
 
 .PHONY: generate-server start-server prepare-server run-test stop-server restart-server
 generate-server: