Use httpMethod instead of type for AJAX get/post request property

Problem/Motivation

See #956186-189: Allow AJAX to use GET requests.

'method' has been in use for a long time. The original patch used 'type', but maybe we could change that to 'httpMethod'. If we make the change before 10.1.x, it won't be an API change.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet