[Feature] Hide Discord link for non-admins on web UI

[ddshd]

I have searched the existing feature requests, both open and closed, to make sure this is not a duplicate request.

• Yes

The feature

Only show the following Discord link for admin users:

immich/web/src/lib/modals/HelpAndFeedbackModal.svelte

Lines 45 to 55 in 571504a

	<div>
	<a href="https://discord.immich.app" target="_blank" rel="noreferrer">
	<Icon path={discordPath} viewBox={discordViewBox} class="inline-block" size="1.5em" />
	<p
	class="font-medium text-immich-primary dark:text-immich-dark-primary text-sm underline inline-block"
	id="github-label"
	>
	{$t('discord')}
	</p>
	</a>
	</div>

The modal makes it seem like non-admins should be using Discord for their support, instead of asking their admin.

Admins should be okay to see and use the link since they are more likely able to provide more information to track down a bug.
Documentation and source links are pretty harmless for users to look at if they want to.

Places in the web where user.isAdmin is used (to borrow the logic from):
https://github.com/search?q=repo%3Aimmich-app%2Fimmich+path%3Aweb%2F+%24user.isAdmin&type=code

Platform

• Server
• Web
• Mobile