Add hooks for plugins to show custom Graph Source and custom Template URL (List View)

[YongBoLiu]

Feature Request

Yes, after auto created huge number of graphs without graph template in my plugin, it shows 'Not Templated' in both 'Source Type' and 'Source name' fields. In Graphs->List View.

We need to provide hooks to customize the 'Source Type' and 'Source name' fields for plugins. Because these graphs without graph template can have some special property for plugin.

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If no hooks for this, plugin develop have to update the graphs.php again and again after cacti core upgraded.

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Additional context

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The same hooks needed as we did in In Console->Management->Graphs. As in ticket #3513 .

[YongBoLiu]

Pull request #3944 created for this.