Add OpenGitOps to CNCF Sandbox project website and landscape

[scottrigby]

The project listings on cncf.io have switched. It's now the landscape that gets projects on the website.

• [x] Open a PR for https://github.com/cncf/landscape/blob/master/landscape.yml https://github.com/cncf/landscape/pull/2224
• [x] ensure PR is reviewed and merged

Related to

• 14

[scottrigby]

OpenGitOps is now officially listed as a CNCF Sandbox project 😄

• https://www.cncf.io/sandbox-projects/
• https://landscape.cncf.io/card-mode?project=sandbox