Add recurse submodules arg to bootstrap cmd

cmd/flux/bootstrap.go

cmd/flux/bootstrap_git.go

cmd/flux/bootstrap_github.go

cmd/flux/bootstrap_gitlab.go

cmd/flux/create_source_git.go

docs/cmd/flux_bootstrap.md

docs/cmd/flux_bootstrap_git.md

docs/cmd/flux_bootstrap_github.md

docs/cmd/flux_bootstrap_gitlab.md

docs/cmd/flux_create_source_git.md

pkg/manifestgen/sync/options.go

pkg/manifestgen/sync/sync.go