[Module Proposal]: `avm/res/authorization/pim-role-assignment_scope-sub/rg/mg`

### Check for previous/existing GitHub issues/module proposals

- [x] I have checked for previous/existing GitHub issues/module proposals.

### Check this module doesn't already exist in the module indexes

- [x] I have checked for that this module doesn't already exist in the module indexes.

### Bicep or Terraform?

Bicep

### Module Classification?

Resource Module

### Module Name

avm/res/authorization/pim-role-assignment_scope-sub/rg/mg

### Module Details

As the role assignment modules ( for example #1935 ) are being created separately for different scopes I think it would be nice to have the same approach for PIM assignments.

### Do you want to be the owner of this module?

No

### Module Owner's GitHub Username (handle)

_No response_

### (Optional) Secondary Module Owner's GitHub Username (handle)

_No response_