Add gradle to supporting companies

[atomfrede]

Overview of the feature request

Add gradle as supporting company to the new section on the website. I know this section is intended to be for open collective sponsors, but I would say its fair to show gradle there too.

Motivation for or Use Case

They give us free develocity instance and license for both gradle and maven for free.

• Checking this box is mandatory (this is just to show you read everything)

[DanielFran]

@atomfrede Already available here: https://www.jhipster.tech/contributing-companies/

[atomfrede]

@DanielFran Yes true, but I think the contributing companies is a little different imho. We should update it at least and make clear that gradle is supporting us with a paid service for free, so I would put them under supporting companies on the start page.