feat: replace raw alpha warnings with admonitions when generating C8 REST API docs

[pepopowitz]

Description

In camunda/camunda#24340, we removed all docs-specific formatting from the upstream spec. We'd already accounted for adding links in #4541, but we also need to add admonitions for alpha warnings.

This PR turns a text-only alpha warning into a :::note admonition.

This injection has no effect on the current docs spec, because the admonitions are already there -- this is why there are no files changed other than the generation strategy. However, when camunda/camunda#24340 makes it to this project via the weekly spec sync, our spec will be missing admonitions, and we'll want to regenerate with this new step.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.

• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

• My changes require a docs infrastructure review.

[akeller]

This injection has no effect on the current docs spec, because the admonitions are already there -- this is why there are no files changed other than the generation strategy. However, when camunda/camunda#24340 makes it to this project via the weekly spec sync, our spec will be missing admonitions, and we'll want to regenerate with this new step.

If I'm understanding this correctly, we cannot test this quite yet. I can give a handwavy approval now, or we can wait until we have something to test. How would you like to proceed @pepopowitz?

[pepopowitz]

Correct. Let's do the hand-wavy thing for now, and I'll kick off a new sync after it merges, to "test in production" real quickly.

[akeller]

👋 👋

[pepopowitz]

Confirmed in #4581 that this new adjustment works properly.