Update functions docs

[pauljohanneskraft]

Update functions docs

♻️ Current situation & Problem

Unfortunately, I forgot to update the functions docs to reflect the removal of "checkInvitaitonCode" and its replacement "enrollUser".

⚙️ Release Notes

Add a bullet point list summary of the feature and possible migration guides if this is a breaking change so this section can be added to the release notes.
Include code snippets that provide examples of the feature implemented or links to the documentation if it appends or changes the public interface.

📚 Documentation

Please ensure that you properly document any additions in conformance to Spezi Documentation Guide.
You can use this section to describe your solution, but we encourage contributors to document your reasoning and changes using in-line documentation.

✅ Testing

Please ensure that the PR meets the testing requirements set by CodeCov and that new functionality is appropriately tested.
This section describes important information about the tests and why some elements might not be testable.

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