Allow icons for custom Help Desk filter names, consistent with default filters

Default filters like “My Mentions” and “Snoozed” display clean, native icons, but when creating a custom filter, only emojis are available.

Emojis feel visually inconsistent with the rest of the interface and can disrupt the polished look of the sidebar.

Allowing users to assign the same icon set used by default filters to their custom ones would create a more cohesive, professional experience in my mind.