Method for spec structures to set default values

[renehernandez]

When syncing an app specifcation without fields like instance_size_slug or instance_count declared, those fields are assigned default values during the App creation in the Platform. That logic should be baked in Spec structs (AppStaticSiteSpec, AppServiceSpec, etc). Some of the default values I have noticed:

• scope field in the envs section
• routes (when the internal_ports field is empty)
• instance_size_slug
• instance_count
• region

I am currently setting the expected default values as part of the appfile diff invocation at https://github.com/renehernandez/appfile/blob/main/internal/apps/app_spec.go, so that the diffs show the expected values, without being messed up by the lack of the default values

[kamaln7]

Hey @renehernandez I missed this one. This will be part of #415

[kamaln7]

Merged #422 which fixes this.