Add loader if center value hasn't rendered

[codemist]

References:

Jira: MNTOR-3154

Description

Screenshot (if applicable)

https://github.com/mozilla/blurts-server/assets/13066134/51987059-5187-4e87-bbc5-4114505e443a

How to test

Checklist (Definition of Done)

• [ ] Localization strings (if needed) have been added.
• [ ] Commits in this PR are minimal and have descriptive commit messages.
• [ ] I've added or updated the relevant sections in readme and/or code comments
• [ ] I've added a unit test to test for potential regressions of this bug.
• [ ] Product Owner accepted the User Story (demo of functionality completed) or waived the privilege.
• [ ] All acceptance criteria are met.
• [ ] Jira ticket has been updated (if needed) to match changes made during the development process.
• [ ] Jira ticket has been updated (if needed) with suggestions for QA when this PR is deployed to stage.

[Vinnl]

I got nerd-sniped into trying to find out why the colours wouldn't show up, and found out that it's because our Content Security Policy doesn't allow defining styles via the style attribute. One potential solution is to widen our CSP policy, which I've submitted a PR for here: https://github.com/mozilla/blurts-server/pull/4531

I'm not sure I'm able to reproduce what the issue is with the center value, but possibly that PR also solves that?

[github-actions[bot]]

Preview URL :rocket: : https://blurts-server-pr-4512-mgjlpikfea-uk.a.run.app

[github-actions[bot]]

Preview URL :rocket: : https://blurts-server-pr-4512-mgjlpikfea-uk.a.run.app

[github-actions[bot]]

Preview URL :rocket: : https://blurts-server-pr-4512-mgjlpikfea-uk.a.run.app

[rhelmer]

@codemist are you still working on this one?

[Vinnl]

I'm assuming no, and that this has stalled/been de-prioritised, so closing for now.