feat: Add template icon to the workspaces page (#3612)

This removes the last built by column from the page. It seemed
cluttered to have both on the page, and is simple enough to
click on the workspace to see additional info.

codersdk/workspaces.go

@@ -24,6 +24,7 @@ type Workspace struct {
 	OwnerName         string         `json:"owner_name"`
 	TemplateID        uuid.UUID      `json:"template_id"`
 	TemplateName      string         `json:"template_name"`
+	TemplateIcon      string         `json:"template_icon"`
 	LatestBuild       WorkspaceBuild `json:"latest_build"`
 	Outdated          bool           `json:"outdated"`
 	Name              string         `json:"name"`