Update logic for metric publisher topic name

[samfreund]

getName() gives the full string, not just the title of the topic. Therefore, it needs to be split in order to get the title of the topic.

Let this be a lesson to test things when something has changed before they are merged.

Meta

Merge checklist:

• Pull Request title is short, imperative summary of proposed changes
• The description documents the what and why
• If this PR changes behavior or adds a feature, user documentation is updated
• If this PR touches photon-serde, all messages have been regenerated and hashes have not changed unexpectedly
• If this PR touches configuration, this is backwards compatible with settings back to v2024.3.1
• If this PR touches pipeline settings or anything related to data exchange, the frontend typing is updated
• If this PR addresses a bug, a regression test for it is added

[mcm001]

I don't see a good way to test or shim this logic so no tests needed here imo. Hope you tested this manually.