Make method configurable between GET and POST

Problem/Motivation

Currently the form is forcing to use GET to post the data. The problem is that the search of users is then in GET parameters. If the site is using tracking tools such as Google analytics etc..., then the site can become illegal because user search is personal data and cannot be collected for privacy reasons in some regions.

Steps to reproduce

Proposed resolution

Make it configurable to allow to use post. The default should stay GET to avoid affecting existing site using the module.

Remaining tasks

User interface changes

API changes

Data model changes