Prepare: run E2E smoketests with GitHub actions (#23301)

- Port E2E testing scripts from cypress-ui-automation
- Move server to docker-compose, move E2E images to ecrpublic
* Integrate General channel renaming, fixes
- Add local automation-dashboard
- Add readme
- Add E2E smoketests
- Bump postgres to 12

---------

Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Saturnino Abril <saturnino.abril@gmail.com>
Co-authored-by: Antonis Stamatiou <stamatiou.antonis@gmail.com>

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

@@ -0,0 +1,46 @@
+#!/bin/bash
+set -e -u -o pipefail
+cd $(dirname $0)
+. .e2erc
+
+# Set required variables
+TEST_FILTER_DEFAULT='--stage=@prod --group=@smoke'
+TEST_FILTER=${TEST_FILTER:-$TEST_FILTER_DEFAULT}
+
+# Print run information
+mme2e_log "Printing Cypress container informations"
+${MME2E_DC_SERVER} exec -T -u $MME2E_UID -- cypress node -p 'module.paths'
+${MME2E_DC_SERVER} exec -T -u $MME2E_UID -- cypress bash <<"EOF"
+cat <<INNEREOF
+node version:    $(node -v)
+npm version:     $(npm -v)
+debian version:  $(cat /etc/debian_version)
+user:            $(whoami)
+chrome:          $(google-chrome --version || true)
+firefox:         $(firefox --version || true)
+INNEREOF
+EOF
+
+# Initialize cypress report directory
+mme2e_log "Prepare Cypress: clean and initialize report and logs directory"
+${MME2E_DC_SERVER} exec -T -u $MME2E_UID -- cypress bash <<EOF
+rm -rf logs results
+mkdir -p logs
+mkdir -p results/junit
+touch results/junit/empty.xml
+echo '<?xml version="1.0" encoding="UTF-8"?>' > results/junit/empty.xml
+EOF
+
+# Run cypress test
+# No need to collect its exit status: if it's nonzero, this script will terminate since we use '-e'
+if ${MME2E_DC_SERVER} exec -T -u $MME2E_UID -- cypress bash -c '[ -n "${AUTOMATION_DASHBOARD_URL}" ]'; then
+	mme2e_log "AUTOMATION_DASHBOARD_URL is set. Using run_test_cycle.js for the cypress run"
+	${MME2E_DC_SERVER} exec -T -u $MME2E_UID -- cypress node --trace-warnings generate_test_cycle.js ${TEST_FILTER}
+	${MME2E_DC_SERVER} exec -T -u $MME2E_UID -- cypress node run_test_cycle.js | tee ../cypress/logs/cypress.log
+else
+	mme2e_log "AUTOMATION_DASHBOARD_URL is unset. Using run_tests.js for the cypress run"
+	${MME2E_DC_SERVER} exec -T -u $MME2E_UID -- cypress node run_tests.js ${TEST_FILTER} | tee ../cypress/logs/cypress.log
+fi
+
+# Collect server logs
+${MME2E_DC_SERVER} exec -T -- server cat /mattermost/logs/mattermost.log >../cypress/logs/mattermost.log