Do not allow two plugins with the same name

[mykhailopylyp]

As was noticed in #10328 we assume that plugin names are different.
We can easily keep this invariant now when we don't have third-party plugins. But in the future, we will need graceful handling for this.

[htcfreek]

In the json we have the uuid. Could we use it for identification or add a ShortIdentifier (e.g. ShortIdentifier=MicrosoftWinSearch) property?

[enricogior]

@htcfreek
no because we need to be able to report the telemetry plugin usage and the plugins must have human readable name.