Move metrics subtable to root PV table

[samfreund]

Description

The metrics subtable is now published under the main PV table, as publishing it under the coproc table means that it's viewed as another MAC address, which it isn't.

Additionally adds a note that the coproc table is meant for MAC address stuff only.

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