Use the second case with a separate namespace per tenant.

Different configurations

You have designed a solution with a separate database for each tenant. You can run the same container image for the tenants but the should use different configurations e.g. they have different address to the database. See Twelve factor - externalize configuration.

We must always create a new service's container for each tenant. Although if load is low we could use one general container for all tenants

You can easily create the same service for each tenant using Kubernetes declarative Deployment manifests. You can also assign only the resources that is needed for each tenant, e.g. variations in number of replicas or different CPU or Memory resources.

Route error information to a central service

We have single entry point for detect errors

You should always route observability information, e.g. logs, metrics and events to a central service for your cluster.

Isolate tenants

In addition, if you have separate namespaces for tenants, you can isolate them more using Network Policies