feat(web): Add "set as featured" option for an asset

[IMBeniamin]

Description

This is a QoL feature that enables a user to set the featured photo of a person while inspecting (in full screen) said person.
This is an alternative flow to the currently existing one: person -> three dots -> select featured photo
It is now possible to set a featured photo by doing this:
person -> photo -> three dots -> use this as featured photo
The option is hidden in all views except when a person is provided to the asset-grid (i.e. the people/id page)

Note: I have followed the "set as album cover" implementation for this. The prop is propagated from the asset-grid all the way down to the asset-viewer-nav-bar. I do not like the fact that the handle function has been duplicated in both cases, but at least it's consistent.
[handleSelectFeaturePhoto]
(https://github.com/IMBeniamin/immich/blob/de39bf2b1701069b33949d5da3e0f47cdd338672/web/src/lib/components/asset-viewer/actions/set-person-featured-action.svelte#L19)
handleSelectFeaturePhoto

How Has This Been Tested?

• Open the asset viewer from the timeline. Option should NOT be visible
• Open the asset viewer from the album asset grid view. Option should NOT be visible
• Open the asset viewer from the people page. Option IS visible
• Feature photo is updated after clicking the set as featured photo option

Screenshots

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable

[bo0tzz]

Neat! How does this behave if there are multiple people in the photo?

[IMBeniamin]

Neat! How does this behave if there are multiple people in the photo?

The action is only shown when navigating to the asset viewer from a person. Consequently the person which is updated is always the one from which the asset grid has been created.

Example:

https://<immich_host>/people/c96b6bb7-553a-434b-867f-843f0ec89e6c/photos/a65bacc5-85e9-4d81-8e67-71fa4fd6b282?previousRoute=%2Fpeople
Would update the featured photo for c96b6bb7-553a-434b-867f-843f0ec89e6c

[jrasm91]

LGTM