Update templates.json for Event Grid templates to use 3.0.0 extension version

[mattchenderson]

The package references for all Event Grid templates should be updated to use the new extension version

[fabiocav]

@AnatoliB assigning some of these extension template update items to you for triage.

[shreyabatra4]

Hi @JoshLove-msft, can you please help to take a look at this issue for defaulting new function applications to Track 2 extensions? The requested action is the same as for EventHubs (issue #1114) - to update the templates such that they refer to the extension bundle version "[3.*, 4.0.0)" in the file 'host.json'. and to update the nuget references in the Track 2 templates for .NET to reference the Track 2 extensions.