[Ops] Fix serverless startup issue around importing @kbn/dev-utils

[delanni]

Summary

Fixes kibana-serverless issues of this nature: https://elastic.slack.com/archives/C04L3JE8LV6/p1693450827486199 or https://elastic.slack.com/archives/C04L3JE8LV6/p1693473384616049

After #162673 - serverless images started breaking: https://github.com/elastic/serverless-gitops/commits/main/services/kibana/versions.yaml
The issue is probably that the library @kbn/dev-utils is a devDependency, thus it doesn't show up in the serverless image, but it's required for the serve script. This doesn't show up locally (or probably in other kibana distros) because dev/prod dependencies are also installed together.

To solve this, I inlined the token (as it doesn't depend on anything else, it's just saved in a central place for code deduplication) - if it's a better solution, we can just move the @kbn/dev-utils to the prod dependencies, but I don't know enough about the context to make that decision.

• fix(kibana-serverless): inline dev service account token - in the serverless images the @kbn/dev-utils package is not linked

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[watson]

There's probably a better way to do this without resorting to duplication, but currently I can't see it. I'm approving for now to unblock - then we can follow up later to clean it up.

[kibana-ci]

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Metrics [docs]

✅ unchanged

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