Document CDN endpoint for server subs assets (#5856)

* Document CDN endpoint for server subs assets

Server subs assets use the path: `:app_id/store/:asset_id`, while the actual asset IDs cannot be managed or fetched by bots, this should be documented for completeness in case an app ever wishes to refer to these assets.

* Updated wording & positioning

Endpoint is used for store page assets & repurposed for server subs. For consideration of legacy store pages & other implementations (like sticker pack banners), this naming & position would be more accurate.

Author: panley01

docs/Reference.md

@@ -325,6 +325,7 @@ Discord uses ids and hashes to render images in the client. These hashes can be
 | Application Cover           | app-icons/[application_id](#DOCS_RESOURCES_APPLICATION/application-object)/[cover_image](#DOCS_RESOURCES_APPLICATION/application-object).png                                                                                                                      | PNG, JPEG, WebP      |
 | Application Asset           | app-assets/[application_id](#DOCS_RESOURCES_APPLICATION/application-object)/[asset_id](#DOCS_TOPICS_GATEWAY_EVENTS/activity-object-activity-assets).png                                                                                                                  | PNG, JPEG, WebP      |
 | Achievement Icon            | app-assets/[application_id](#DOCS_RESOURCES_APPLICATION/application-object)/achievements/[achievement_id](#DOCS_GAME_SDK_ACHIEVEMENTS/data-models-user-achievement-struct)/icons/[icon_hash](#DOCS_GAME_SDK_ACHIEVEMENTS/data-models-user-achievement-struct).png | PNG, JPEG, WebP      |
+| Store Page Asset            | app-assets/[application_id](#DOCS_RESOURCES_APPLICATION/application-object)/store/asset_id                                                                                                                                                                       | PNG, JPEG, WebP      |
 | Sticker Pack Banner         | app-assets/710982414301790216/store/[sticker_pack_banner_asset_id](#DOCS_RESOURCES_STICKER/sticker-pack-object).png                                                                                                                                               | PNG, JPEG, WebP      |
 | Team Icon                   | team-icons/[team_id](#DOCS_TOPICS_TEAMS/data-models-team-object)/[team_icon](#DOCS_TOPICS_TEAMS/data-models-team-object).png                                                                                                                                      | PNG, JPEG, WebP      |
 | Sticker                     | stickers/[sticker_id](#DOCS_RESOURCES_STICKER/sticker-object).png \*\*\* \*\*\*\*                                                                                                                                                                                 | PNG, Lottie, GIF     |