Snap deprecation situation can be improved

Hello, a snap packager here and would like to have some suggestions on how to improve the situation.

Currently(2024/8/21), the snap is still searchable in the store:

```txt
$ snap find lsd
Name Version Publisher Notes Summary
lsd 0.16.0 peltoche - A ls command with a lot of pretty colors.
```

and the snap listing page shows no signs of deprecation, aside from the old release date:

```txt
$ snap info lsd
name: lsd
summary: A ls command with a lot of pretty colors.
publisher: Pierre Peltier (peltoche)
store-url: https://snapcraft.io/lsd
contact: peltoche@halium.fr
license: unset
description: |
lsd is a ls command including pretty icons based on nerd-font.
commands:
- lsd
snap-id: wg6vD3jHxl87UtHKsX9obkJMYCed1JX3
tracking: latest/stable
refresh-date: today at 00:12 CST
channels:
latest/stable: 0.16.0 2019-08-02 (62) 929kB -
latest/candidate: ↑
latest/beta: ↑
latest/edge: ↑
```

I would like to suggest that anyone who has store backstage access do the following actions to allow the users to recognize the deprecation status of the snap more easily:

* In the store backstage > Settings tab > Visibility panel, select `Unlisted` so that the snap won't be enumerated from the search results:
* In the store backstage > Listing tab > Listing details > Description field, add a note that the snap has been discontinued, with a link to this issue.

Start with the Snapcraft settings and listing pages linked in the issue, especially the Visibility panel and Listing details description field. Verify the snap is no longer enumerated by search and that its listing clearly states it is discontinued and links back to issue #1089.

Written by the indexing model from the issue text.