Provide script to assign a role to a resource

**Is your feature request related to a problem? Please describe.**
Since the current script `New-AzResourceGroupRoleAssignment` only allows for the creation of a new role assignment to a resource group, a separate script `New-AzResourceRoleAssignment` should be created to assign a new role based on the ObjectId or ResourceGroupName/Resource-combo to a specific resource.

**Describe the solution you'd like**
The script should accept the following parameters:
- TargetResourceGroupName (mandatory)
- TargetResourceName (mandatory)
- TargetResourceType (mandatory)
- RoleDefinitionName (mandatory)
- ObjectId
OR _(see #150)_
- ResourceGroupName AND ResourceName

**Describe alternatives you've considered**
Extend the existing function, however then the name should be changed, which means introducing a breaking change.

Start by inspecting the existing New-AzResourceGroupRoleAssignment script and the related requirements in issue #150. Confirm how resource groups, resources, role definitions, and ObjectId or ResourceGroupName/ResourceName inputs are handled; done means a separate New-AzResourceRoleAssignment script accepts the required parameters and assigns the role to a specific resource.

Written by the indexing model from the issue text.