LP plugins can leverage new http server during migration

[mshustov]

Summary

this PR allows legacy plugins to use NP routing during migration.
Parent issue: #33775

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

• [ ] This was checked for cross-browser compatibility, including a check against IE11
• [ ] Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• [ ] Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• [ ] This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-platform

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[epixa]

We shouldn’t move forward with this until we have http route authentication on the new platform, otherwise developers can accidentally bypass security. Unless I’m missing something?

[mshustov]

@epixa this a preparational work to allow Security team to start using NP. actually we can put this PR on block until they are ready to switch

[mshustov]

closed in favour of #39047