Ensure `New metacluster` does not need to be clicked to save default metacluster remappings in Pixie

**Describe the bug**

This addresses a known bug in the metacluster step of Pixie that requires this button to be clicked to save out the default mappings. If this button is not clicked, then the following remapping cell cannot be run because no mapping exists. This can confuse users who want to use the default mappings, even though we've outlined it in the documentation.

**Expected behavior**

Proposing that the default mappings should automatically be saved so the users always have "something" they can run. We should inform them in the documentation that this is the default functionality.

**To Reproduce**

Run the pipeline as is.