Show memory on clusters list

What does this MR do?

This adds a Total memory (GB) column to the clusters list table.

This MR is an iteration towards completing #207031 (closed)

Note: We already have existing tests to ensure that the columns are displayed correctly.

All changes in this MR is behind the clusters_list_redesign feature flag.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

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