Improvement: A way to support map[string]json secrets

[super-harsh]

Describe the current behavior

Currently we don't have support for map[string]json secrets

Describe the improvement

ASO should support map[string]json secrets.
Discussion: #3743 (comment)

[matthchr]

This would primarily be used by VM extensions

[matthchr]

This is primarily talking about for inputs. #2555 will support maps for outputs.

[matthchr]

We haven't heard much from users about this lack yet, and in fact it seems like even most extensions don't support the nested-map of inputs in their ARM API...

Planning on leaving this unimplemented until there's a user request.