Bump up the minimum required MySQL version (#25465)

MySQL 5.7 is at end of life.

https://mattermost.atlassian.net/browse/MM-55589

```release-note
We bump up minimum MySQL version to be 8.0.0
```


Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Ibrahim Serdar Acikgoz <serdaracikgoz86@gmail.com>

server/channels/store/sqlstore/store.go

@@ -52,8 +52,7 @@ const (
 	// 9.6.3 would be 90603.
 	minimumRequiredPostgresVersion = 110000
 	// major*1000 + minor*100 + patch
-	minimumRequiredMySQLVersion    = 5712
-	minimumRecommendedMySQLVersion = 8000
+	minimumRequiredMySQLVersion = 8000
 
 	migrationsDirectionUp   migrationDirection = "up"
 	migrationsDirectionDown migrationDirection = "down"
@@ -1232,9 +1231,6 @@ func (ss *SqlStore) ensureMinimumDBVersion(ver string) (bool, error) {
 			return false, fmt.Errorf("cannot parse MySQL DB version: %w", err2)
 		}
 		intVer := majorVer*1000 + minorVer*100 + patchVer
-		if intVer < minimumRecommendedMySQLVersion {
-			mlog.Warn("The MySQL version being used is EOL. Please upgrade to a later version.", mlog.Int("current_version", intVer), mlog.Int("minimum_recommended_version", minimumRecommendedMySQLVersion))
-		}
 		if intVer < minimumRequiredMySQLVersion {
 			return false, fmt.Errorf("Minimum MySQL version requirements not met. Found: %s, Wanted: %s", versionString(intVer, *ss.settings.DriverName), versionString(minimumRequiredMySQLVersion, *ss.settings.DriverName))
 		}

server/channels/store/storetest/settings.go

@@ -22,10 +22,10 @@ import (
 )
 
 const (
-	defaultMysqlDSN        = "mmuser:mostest@tcp(localhost:3306)/mattermost_test?charset=utf8mb4,utf8&readTimeout=30s&writeTimeout=30s&multiStatements=true&maxAllowedPacket=4194304"
+	defaultMysqlDSN        = "mmuser:mostest@tcp(localhost:3306)/mattermost_test?charset=utf8mb4&readTimeout=30s&writeTimeout=30s&multiStatements=true&maxAllowedPacket=4194304"
 	defaultPostgresqlDSN   = "postgres://mmuser:mostest@localhost:5432/mattermost_test?sslmode=disable&connect_timeout=10"
 	defaultMysqlRootPWD    = "mostest"
-	defaultMysqlReplicaDSN = "root:mostest@tcp(localhost:3307)/mattermost_test?charset=utf8mb4,utf8\u0026readTimeout=30s"
+	defaultMysqlReplicaDSN = "root:mostest@tcp(localhost:3307)/mattermost_test?charset=utf8mb4\u0026readTimeout=30s"
 )
 
 func getEnv(name, defaultValue string) string {