UI Request: Enhance to support Bulk Delete Template

##### ISSUE TYPE

* Feature Idea

##### COMPONENT NAME

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Templates GUI
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##### CLOUDSTACK VERSION

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4.19.0
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##### CONFIGURATION

##### OS / ENVIRONMENT

##### SUMMARY

Our company widely uses Autoscale Groups, which results in lots of templates.

Over time, we have more than 100 Templates created, due to the repetitive process of creating a template each time we have an update which we need to apply to our Autoscale Groups.

But these templates end up taking a large amount of space in the secondary storage. In order to clean this up, we currently have to click on to each tempalte, and manually delete it from each zone, then repeat for the next template. Its very time consuming .

So this is a feature idea to enhance the GUI to support Bulk Template Creation. Very similar to how there are checkboxes besides each VM in the Instance Page, which you can have tick to execute bulk operations.

There is a scenario where the Templates will be in multiple zones. In this case, whena bulk delete is executed, the popup should include a checkbox to ask the user if the template should be deleted from all zones, or only from the selected zone.

_PS: Or, if there is a way to create a new template by overriding the existing template, i think that would be a pretty great solution too._

##### STEPS TO REPRODUCE

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##### EXPECTED RESULTS

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To be able to conveniently bulk delete templates to save on Secondary Storage space.
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##### ACTUAL RESULTS

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Have to delete the template one by one.
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