refactor!: set default outbound content type to didcomm v1 (#1314)

Signed-off-by: Timo Glastra <timo@animo.id>

BREAKING CHANGE:

Agent default outbound content type has been changed to DIDComm V1. If you want to use former behaviour, you can do it so by manually setting `didcommMimeType` in `Agent`'s init config:

```
  const agent = new Agent({ config: { 
     ...
     didCommMimeType: DidCommMimeType.V0
  }, ...  })
```

packages/core/src/agent/AgentConfig.ts

@@ -62,7 +62,7 @@ export class AgentConfig {
   }
 
   public get didCommMimeType() {
-    return this.initConfig.didCommMimeType ?? DidCommMimeType.V0
+    return this.initConfig.didCommMimeType ?? DidCommMimeType.V1
   }
 
   /**