Fleet Images

[manno]

Gitjob is now in the fleet repo. However, we are missing system registry support and a way to set gitjob.tag to fleet's version. The git k8s job still uses two images, instead of one and the CLI is downloaded to downstream clusters, where it is never used.

The Windows agent image has a git binary, which is unused.

• [x] move gitjob binaries into fleet image
• [x] move fleet cli from agent to fleet image
• [x] remove gitjob.tag from helm chart
• [x] remove Windows agent Dockerfile and corresponding Windows docs
• ...