[Guided onboarding] Change the API prefix to /internal

[yuliacech]

Summary

Fixes #155611
This PR changes the API prefix to indicate that the endpoints are intended for internal use only. The plugin has been setup incorrectly initially with the prefix /api that is intended for a public API. There should not be any changes to the UI or functionality of the plugin.

Release Note

Fixed the guided onboarding API prefix to indicate that it's intended for internal use

[elasticmachine]

Pinging @elastic/platform-onboarding (Team:Journey/Onboarding)

[alisonelizabeth]

Change LGTM. Did not test locally. Thanks for fixing this!

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 51c4005

Metrics [docs]

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
guidedOnboarding	27.2KB	27.2KB	+5.0B

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	17	19	+2
securitySolution	397	400	+3
total			+5

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	18	20	+2
securitySolution	477	480	+3
total			+5

History

• 💛 Build #122953 was flaky 1e4c7d7
• 💛 Build #122896 was flaky 8c4ef01
• 💔 Build #122884 failed 995185f
• 💔 Build #122564 failed 87f9e40
• 💔 Build #122526 failed 7599cb6

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@elasticmachine merge upstream

[stephmilovic]

LGTM!