move ksctl code

[MatousJobanek]

This PR moves the code of sandbox-cli, its assets, and go.mod & go.sum files with these changes:

• renames the module and all related package imports from github.com/codeready-toolchain/sandbox-sre to github.com/kubesaw/ksctl
• it doesn't include the install & configure commands - they require the assets to be present in the binary, but these assets should stay in the sandbox-sre
• drops all references to the domains of sandbox instances
• adds cmd/ksctl/main.go next to cmd/sandbox-cli/main.go so it builds/installs both, ksctl as well as sandbox-cli.

To be done in the following PRs:

• mark the sandbox-cli as deprecated
• rename all references to sandbox-cli everywhere in the code
• rename/drop all references to sandbox-sre

[MatousJobanek]

Looks good overall. Are we planning to keep the provider: sandbox-sre labels or change them to ksctl?

@rajivnathan already mentioned that in the description ;-) there is gonna be many PR so remove all sandbox references, it will take some time

Looks Good, i think we would be raising follow up PRs for change of sandbox in file name to something relative to ksctl ? eg. pkg/assets/sandbox_config.go. change the name to something pkg/assets/ksctl_config.go ?

The same answer is for you @fbm3307. We will remove the sandbox references in the following PRs. Let's just keep in mind that we need to stay backward compatible for some time.