Disallow GET requests for actionURLs

If the URL as rendered by the <hst:actionURL /> tag is performed as GET request (e.g. by calling the URL from the browser), the components doAction() method is called.

This is unexpected and probably not desirable: we recommend using POSTs for action URLs in [1].

Note that for <form> elements with a method=get atribute, a submit will not lead to calling doAction() because the _hn:type=action parameter is not present in the request (only form parameters are sent).

[1] https://documentation.bloomreach.com/library/concepts/component-development/hst-2-forms.html