[WIP] Add calendar delegation feature in sidebar

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Delegation prompt

We need to implement that calendar delegation feature. Currently the backend already supports this by having the calendar-proxy-read and calendar-proxy-write principal groups in caldav.

What needs to be added is firstly a frontend for this,:

1. add an element in the sidebar between settings and trash bin called delegation

when clicked it will open an ncmodal containing title Delegation, then an NcFormGroup with title Delegates and subtitle Allow users to manage you calendar events and invitation on your behalf.

Inside the group you will have NcListItem elements with the email of the delegatee to the left and an x to the right. The tooltip for the x is revoke access. When the X button is clicked, a confirmation dialog appears: "Revoke access? {email address} will no longer be able to act on your behalf" with the options "Cancel" and "Revoke".

Underneath add the add delegate button, with which a dialog appears with an nctextfield labelled select a user, and underneath a description with “They will be able to manage your calendar events and invitations on your behalf.

2. Delegated calendars would show up under their own section in the sidebar, "Delegated".

Look into this link nextcloud/server#16666 and see how delegation has been implemented in the server repository if you need help

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