SMALL: DRY Service Definitions in `helm`

[ranchodeluxe]

Background

After getting the initial draft services up it seems the raster, stac and vector services all have about the same structure and can be DRY'd up in some general fashion. What we do know:

• try to avoid using template partials via _helpers.tpl b/c Isayah and I agree it's not very intuitive
• if that can't be avoided we might skip being DRY in favor of readability
• simple loop and using intermediate temp vars might work fine here

AC

• what else besides _helpers.tpl?
• DRY up with different methods
• Gut check on how we feel about the DRY methods