AP-4489: add different error messages for whether client has partner

[agoldstone93]

What

Link to story

Add proof of concept for specific messages depending on whether client has a partner

Client only:

Client and partner:

Checklist

Before you ask people to review this PR:

• Tests and rubocop should be passing: bundle exec rake
• Github should not be reporting conflicts; you should have recently run git rebase main.
• There should be no unnecessary whitespace changes. These make diffs harder to read and conflicts more likely.
• The PR description should say what you changed and why, with a link to the JIRA story.
• You should have looked at the diff against main and ensured that nothing unexpected is included in your changes.
• You should have checked that the commit messages say why the change was made.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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0.0% Duplication

[RoseSAK]

This looks good to me although I'm thinking it will be quite a lot of work to manually implement the separate client/partner error messages, just because I think there will be quite a few affected pages? But I'm not sure that there's a better/easier solution so happy to go with this if everyone else is 👍