Support default config at the namespace level

[calebschoepp]

Problem

If a user has wants to deploy many SpinApps into their cluster it is likely that a portion of the configuration for each SpinApp will be duplicated. For example you may want to provide runtime config to every single Spin app that configures the CosmosDB instance it should use as a KV provider.

Potential solution

Provide a way to configure default config for a namespace such that any SpinApp in that namespace inherits that default config.

Considerations

• Where would this default config live? On SpinAppExecutor? On a new CR? Somewhere else?
• What configuration would we want to allow to set defaults for. Runtime config seems like an obvious choice. Most of the other fields of the SpinApp CRD seem like things that would be useful to set defaults for too.

[calebschoepp]

CC @radu-matei