Warn before applying issue templates

Currently changing issue templates will replace content without warning even if the template has been edited.

If a user tries to apply a template and the have not manually modified the content of the description field (added or removed text), the chosen template should automatically replace that content without asking for confirmation. For example, if the user has not changed the original description template (“Before raising an issue to the GitLab Community Edition…”), it should be automatically replaced with the chosen template.
If a user tries to apply a template and they have indeed modified the content of the description field (added or removed text), an alert should be shown asking if they want to apply the chosen template (which will discard their changes) or cancel:

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