Update OCI's creation message

[momesgin]

Describe the bug

As per requested by the team who worked on the OCI feature, we should update the current message on the OCI repository creation page. It's basically just removing For better performance from the message.

Current message:

For better performance, add OCI URLs that contain ONLY helm charts. For example oci://test.rancher.io/charts or oci://test.rancher.io/charts/mychart. The list of charts available from the repository is updated every 6 hours. Scanning directories with a large number of artifacts may degrade performance considerably.

Updated message:

Add OCI URLs that contain ONLY helm charts. For example oci://test.rancher.io/charts or oci://test.rancher.io/charts/mychart. The list of charts available from the repository is updated every 6 hours. Scanning directories with a large number of artifacts may degrade performance considerably.

[momesgin]

@gaktive I've added a 2.10.0 milestone as it's a minor change, but please let me know if I should change that