Feature request: Provide a way to alias commands in bulk

Currently, one can only alias commands one at a time by selecting a command's verb and/or subject, see https://github.com/Azure/autorest.powershell/blob/master/docs/directives.md#cmdlet-aliasing.

### Proposal
#### Option 1
Allow `alias:` have access to the match group of a `subject:` e.g.:
``` yml
- where:
subject: (.*)(WindowsUpdates)(.*)
set:
alias: ${verb}-Mg$1WU$3
```
#### Option 2
Add a rename directive for alias e.g.
``` yml
- where:
alias: Get-(.*)WindowsUpdates(.*)
set:
alias: Get-$1WU$3
```