Rename `gotk` binary to `flux`

.github/workflows/bootstrap.yaml

.github/workflows/docs.yaml

.github/workflows/e2e.yaml

.goreleaser.yml

Makefile

README.md

cmd/flux/bootstrap.go

cmd/flux/bootstrap_github.go

cmd/flux/bootstrap_gitlab.go

cmd/flux/check.go

cmd/flux/completion.go

cmd/flux/completion_bash.go

cmd/flux/completion_fish.go

cmd/flux/completion_powershell.go

cmd/flux/completion_zsh.go

cmd/flux/create.go

cmd/flux/create_alert.go

cmd/flux/create_alertprovider.go

cmd/flux/create_helmrelease.go

cmd/flux/create_kustomization.go