Geo Sites - Unknown Replication WAL bug

What does this MR do and why?

Closes #356323 (closed)

This change fixes a bug where the Replication WAL shows unknown when the value is 0. 0 is a falsey value in Javascript. So we need to account for it as a valid value.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Fetch and checkout this branch
2. Setup Geo and access your Primary GDK (How to setup Geo)
3. Go to the Geo Sites page (admin/geo/sites)
4. Ensure Replication WAL has a value
5. Set your WAL to 0 (most easily done by spoofing it)
   • Add a line this.node.replicationSlotsMaxRetainedWalBytes = 0 above this line: https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/assets/javascripts/geo_nodes/components/details/primary_node/geo_node_primary_other_info.vue#L30
6. Ensure Replication WAL says 0 bytes rather than Unknown

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