Provide script to upload a certificate in the APIM Certificate store

[mbraekman]

Is your feature request related to a problem? Please describe.
Provide script to upload a certificate in the APIM Certificate store.
This allows you to upload private certificates to be used for authenticating against backend services.

Describe the solution you'd like
In order to upload a private certificate, you need to perform these steps:

• Get APIM Context
• Create new AzApiManagementCertificate referring to the APIM-context.

See: https://docs.microsoft.com/en-us/powershell/module/az.apimanagement/new-azapimanagementcertificate?view=azps-5.5.0

This would have the following parameters:

• ResourceGroupName (resource group containing the APIM instance)
• ServiceName (name of the APIM instance)
• CertificateFilePath (full path to the location of the public certificate)
• CertificatePassword (password for the private certificate)

Target-module:

• Arcus.Scripting.ApiManagement

Describe alternatives you've considered
Manual uploading of private certificates.

[stijnmoreels]

Voorlopig lijkt het password required, dus zullen we voorlopig niet kunnen gebruiken voor public certificates. Right?
Azure/azure-powershell#12571