Dialog files have incorrect $schema

[chrimc62]

Describe the bug

Dialog files have an incorrect $schema. They should be referring to the schema generated through merging, instead they are referring to https://raw.githubusercontent.com/microsoft/BotFramework-Composer/stable/Composer/packages/server/schemas/sdk.schema. We have gone to a lot of work to generate a runtime schema and we should use it, something like: ./schemas/sdk.schema. This will allow validation and intellisense in tools like VS code.