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/scripts/mysql-migration-test.sh

@@ -14,7 +14,7 @@ docker exec -i mattermost-mysql mysql -D migrated -uroot -pmostest -e "INSERT IN
 
 echo "Setting up config for db migration"
 cat config/config.json | \
-    jq '.SqlSettings.DataSource = "mmuser:mostest@tcp(localhost:3306)/migrated?charset=utf8mb4,utf8&readTimeout=30s&writeTimeout=30s"' | \
+    jq '.SqlSettings.DataSource = "mmuser:mostest@tcp(localhost:3306)/migrated?charset=utf8mb4&readTimeout=30s&writeTimeout=30s"' | \
     jq '.SqlSettings.DriverName = "mysql"' > $TMPDIR/config.json
 
 echo "Running the migration"
@@ -22,7 +22,7 @@ make ARGS="db migrate --config $TMPDIR/config.json" run-cli
 
 echo "Setting up config for fresh db setup"
 cat config/config.json | \
-    jq '.SqlSettings.DataSource = "mmuser:mostest@tcp(localhost:3306)/latest?charset=utf8mb4,utf8&readTimeout=30s&writeTimeout=30s"' | \
+    jq '.SqlSettings.DataSource = "mmuser:mostest@tcp(localhost:3306)/latest?charset=utf8mb4&readTimeout=30s&writeTimeout=30s"' | \
     jq '.SqlSettings.DriverName = "mysql"' > $TMPDIR/config.json
 
 echo "Setting up fresh db"