* all: run gofumpt
https://github.com/mvdan/gofumpt
The main appeal for me here is that my (and many other peoples')
editors run this on save, so doing a single diff here
keeps other diffs minimal.
* .github/workflows: add gofumpt checker
* Update OpenSSH server image version and add no penalties configuration
* Refactor SSH configuration paths and update test scripts for public key handling
* Update Docker Compose volumes to remove read-only flag for shared directory
* Remove end-to-end test files and related Docker configuration for CA public cert authentication
