added GSP Configuration for Grails 3.3+

[tonyerskine]

If you use GSP views with the Grails Mail plugin in Grails 3.3 or higher, you need to configure the GSP plugin for the views to render properly. See also: https://stackoverflow.com/questions/69993899/grails-4-mail-plugin-illegalargumentexception-could-not-locate-mail-body/69993900

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
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