Improve narrowing of CKEditor CDN configuration type

[Mati365]

Suggested merge commit message (convention)

Feature: Improve result type of useCKEditorCloud to make CKEditorPremiumFeatures and CKBox non-nullable when proper configuration is passed.
Fix: Rename the languages configuration property to translations in useCKEditorCloud.

MINOR BREAKING CHANGE: The languages configuration property has been renamed to translations in useCKEditorCloud.

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Additional information

Must be released before testing:
ckeditor/ckeditor5-integrations-common#25

PRs family:
ckeditor/ckeditor5-vue#311

const { CKEditorPremiumFeatures } = await loadCKEditorCloud( {
  version: '43.0.0',
  premium: true,
  ckbox: {
    version: '2.5.1'
  }
} );

Before:

CKEditorPremiumFeatures is nullable type.

After:

CKEditorPremiumFeatures is not nullable type because premium: true is passed.

[coveralls]

Pull Request Test Coverage Report for Build e6c91205-231c-40cb-94e3-80e8a2757cf2

Details

• 3 of 3 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 533e89fd-cb29-46af-8ff9-d95e3b47b910:	0.0%
Covered Lines:	582
Relevant Lines:	582

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💛 - Coveralls

[gorzelinski]

I added some nitpicks.

[Mati365]

@gorzelinski done