feat: support icon and description in preset (#18977)

## Description 

This PR adds support for `description` and `icon` fields to
`template_version_presets`. These fields will allow displaying richer
information for presets in the UI, improving the user experience when
creating a workspace.
Both fields are optional, non-nullable, and default to empty strings.

## Changes

* Database migration with the addition of `description VARCHAR(128)` and
`icon VARCHAR(256)` columns to the `template_version_presets` table.
* Updated the `CreateWorkspacePageView` in the UI

Note: UI changes will be addressed in a separate PR

coderd/apidoc/docs.go

@@ -14880,9 +14880,15 @@ const docTemplate = `{
                 "default": {
                     "type": "boolean"
                 },
+                "description": {
+                    "type": "string"
+                },
                 "desiredPrebuildInstances": {
                     "type": "integer"
                 },
+                "icon": {
+                    "type": "string"
+                },
                 "id": {
                     "type": "string"
                 },

coderd/apidoc/swagger.json

@@ -13487,9 +13487,15 @@
 				"default": {
 					"type": "boolean"
 				},
+				"description": {
+					"type": "string"
+				},
 				"desiredPrebuildInstances": {
 					"type": "integer"
 				},
+				"icon": {
+					"type": "string"
+				},
 				"id": {
 					"type": "string"
 				},