13770: Update Documentation: Federated Calendar Shares

[Vedant-Arora]

Clarified that existing federated calendar shares will be deleted when the feature is disabled.

☑️ Resolves outdated admin documentation

• Fix Document: https://github.com/nextcloud/server/pull/55630 #13770

🖼️ Screenshots

[welcome]

Thanks for your first pull request and welcome to the community! Feel free to keep them coming! If you are looking for issues to tackle then have a look at this selection: https://github.com/nextcloud/documentation/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22

[SebastianKrupinski]

/backport to stable32

[SebastianKrupinski]

@Vedant-Arora Thank you!!!

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