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/presets.go

@@ -54,6 +54,8 @@ func (api *API) templateVersionPresets(rw http.ResponseWriter, r *http.Request)
 			Name:                     preset.Name,
 			Default:                  preset.IsDefault,
 			DesiredPrebuildInstances: convertPrebuildInstances(preset.DesiredInstances),
+			Description:              preset.Description,
+			Icon:                     preset.Icon,
 		}
 		for _, presetParam := range presetParams {
 			if presetParam.TemplateVersionPresetID != preset.ID {