Fix typo in the dynamic-plugins docs' package.json configurations

[Zaperex]

Description

Fix typo in dynamic-plugins docs' package.json configurations
The current "recommended" package.json configuration will cause the yarn install and yarn add to fail due to npm:janus-idp/backend-plugin-manager@0.0.5-janus.0 not being a valid package.

There is also a bug in the recommended export-dynamic script, which uses backstage-cli (the package export-dynamic-plugins command does not exist in upstream cli) instead of janus-cli.

Which issue(s) does this PR fix

N/A

PR acceptance criteria

Please make sure that the following steps are complete:

• GitHub Actions are completed and successful
• Unit Tests are updated and passing
• E2E Tests are updated and passing
• Documentation is updated if necessary (requirement for new features)
• Add a screenshot if the change is UX/UI related

How to test changes / Special notes to the reviewer

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