Secrets Management: The implementing folder should be called `SecretsManagementExtension`

[SteveL-MSFT]

Currently, the module expects extensions to be in a folder called ImplementingModule and also the module to have that name. We should call it something more specific like SecretsManagementExtension as we may use this model for other types of extensions in the future.

[JustinGrote]

Either this or use a .psd1 manifest variable in PrivateData or whatnot so the module can designate where the code is.

It would be ideal if a Powershell Script module could just expose a secrets management interface without having to ship an entirely separate module, similar to how DSC works today.

[PaulHigin]

This has been addressed with PR (#39).