Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/build/dotenv/test-schema-validation.env

@@ -0,0 +1 @@
+IS_CI=true

server/build/dotenv/test.env

@@ -0,0 +1,15 @@
+TEST_DATABASE_MYSQL_DSN=mmuser:mostest@tcp(mysql:3306)/mattermost_test?charset=utf8mb4,utf8&readTimeout=30s&writeTimeout=30s&multiStatements=true
+TEST_DATABASE_POSTGRESQL_DSN=postgres://mmuser:mostest@postgres:5432/mattermost_test?sslmode=disable&connect_timeout=10
+TEST_DATABASE_MYSQL_ROOT_PASSWD=mostest
+GOBIN=/mattermost/mattermost-server/bin
+
+CI_INBUCKET_HOST=inbucket
+CI_MINIO_HOST=minio
+CI_INBUCKET_PORT=9001
+CI_MINIO_PORT=9000
+CI_INBUCKET_SMTP_PORT=10025
+CI_LDAP_HOST=openldap
+IS_CI=true
+MM_EMAILSETTINGS_SMTPSERVER=inbucket
+MM_EMAILSETTINGS_SMTPPORT=10025
+MM_ELASTICSEARCHSETTINGS_CONNECTIONURL=http://elasticsearch:9200