### Packages impacted by this PR
- [@azure/notification-hubs]
### Issues associated with this PR
### Describe the problem that is addressed by this PR
Adds a design document for modular design for all projects, adding
subpath exports and extended ESM support
### What are the possible designs available to address the problem? If
there are more than one possible design, why was the one in this PR
chosen?
### Are there test cases added in this PR? _(If not, why?)_
### Provide a list of related PRs _(if any)_
### Command used to generate this PR:**_(Applicable only to SDK release
request PRs)_
### Checklists
- [ ] Added impacted package name to the issue description
- [ ] Does this PR needs any fixes in the SDK Generator?** _(If so,
create an Issue in the
[Autorest/typescript](https://github.com/Azure/autorest.typescript)
repository and link it here)_
- [ ] Added a changelog (if necessary)
Jana R
Matthew Podwysocki