[Feature Request] Suggestion to request to add dialog-attribute

### Existing Component
Yes

### Component Name
Dialog

### Description
Hello! I'm using element-ui in company project, I need to customize dialog-component (e.g] cookie consent dialog, popup).

Therefore dialog need interaction with parent or another components, but element-ui dialog don't support interaction with another components. I customized dialog component for interaction other-components with resizing dialog-wrapper's margin and dialog size (like popup).

I felt inconvenient to customize dialog-component, I'm sure it's not only me, but other people as well. Therefore I suggest to add dialog-attribute to be able interaction.

Thank you to read this issue 😄