CmdLet for updating RunAS of automation HybridWorker group

[MasterKuat]

Description of the new feature

It could be usefull to have a cmdLet like 'Set-AzAutomationHybridWorkerGroup' in order to define à custom credential or undefine it.
Reference of Azure API
https://docs.microsoft.com/en-us/rest/api/automation/hybridrunbookworkergroup/update

Proposed implementation details (optional)

[sphibbs]

@MasterKuat Thanks for the feature request. We will schedule this feature as part of our Az V3 work.