docs: updating initializeApp() TypeScript @example

[EvanLovely]

Hi! Noticed that the initializeApp() TypeScript popups that have example code were using applicationId instead of appId so this updates them! Thanks for the awesome project!

[googlebot]

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[EvanLovely]

@googlebot I signed it!

[googlebot]

CLAs look good, thanks!

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[Feiyang1]

Thanks for the contribution!