ci: refactor SSH testing workflows and job configurations

- Rename workflow from "remote ssh command" to "testing main branch"
- Remove environment variables `FOO` and `BAR`
- Rename job `testing01` to `default-user-name-password`
- Rename step "checkout" to "Checkout code"
- Replace step "correct password but wrong key" with "create new ssh server" using Docker
- Update SSH connection details to use environment variables for host, username, password, and port
- Add new job `check-ssh-key` with steps to add public key to environment and create a new SSH server
- Add new job `support-key-passphrase` with steps to add public key to environment and create a new SSH server
- Add new job `multiple-server` to create and manage multiple SSH servers
- Add new job `support-ed25519-key` with steps to add public key to environment and create a new SSH server
- Add new job `testing-with-env` with steps to add public key to environment and create a new SSH server
- Remove jobs `testing02`, `testing03`, `testing04`, and `testing05`
- Rename workflow in `ssh-server.yml` from "openssh-server" to "testing stable version"

Signed-off-by: appleboy <appleboy.tw@gmail.com>