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/database/dbgen/dbgen.go

@@ -1392,6 +1392,8 @@ func Preset(t testing.TB, db database.Store, seed database.InsertPresetParams) d
 		InvalidateAfterSecs: seed.InvalidateAfterSecs,
 		SchedulingTimezone:  seed.SchedulingTimezone,
 		IsDefault:           seed.IsDefault,
+		Description:         seed.Description,
+		Icon:                seed.Icon,
 	})
 	require.NoError(t, err, "insert preset")
 	return preset