Add log level flag

cmd/gotk/bootstrap.go

cmd/gotk/bootstrap_github.go

cmd/gotk/bootstrap_gitlab.go

cmd/gotk/install.go

cmd/gotk/main.go

docs/cmd/gotk_bootstrap.md

docs/cmd/gotk_bootstrap_github.md

docs/cmd/gotk_bootstrap_gitlab.md

docs/cmd/gotk_install.md