DM-42677: Don't forward visits with instrument=""

[kfindeisen]

This PR adds a filter to avoid fanning out nextVisit messages with an empty instrument, as such messages are unprocessable and result in errors in Prompt Processing.

[dspeck1]

Looks good. To cut a release we need to create a release then add a git tag with the release number. Should we add instructions here or is their another location to put that to avoid re-creating the same instructions (same as for prompt_processing) repo?

[kfindeisen]

Sorry, I don't understand. GitHub releases need an existing tag, and IIRC the web UI will define one if you didn't provide it yourself. How can you create a release and then add a tag? At best, that would mean redefining the tag after the fact.

As for where, the most natural place would be the Playbook in prompt_processing, which already contains instructions for the (old) build process. I see you already added it on lsst-dm/prompt_processing#115, so perhaps we can discuss the details there.

[dspeck1]

To create a tag type the tag name in the Choose a tag field. Thanks. Sound fine to use prompt_processing playbook. I'll add note that it applies to both repos.