Fluxd: Adding a command flag procedure

When adding a new command flag to cmd/fluxd these are the steps to change the installers and documentation:

• add the flag to install/templates
• run make check-generated to update the baked-in templates
• run $GOBIN/fluxctl install --git-url=git@github.com:weaveworks/flux-get-started --git-email=fluxcdbot@users.noreply.github.com --git-user=fluxcdbot to generate example YAMLs
• update deploy/flux-deployment.yaml according to the generated definition
• add the flag description to docs/references/daemon.md
• add the flag to chart/flux/values.yaml
• map the flag in chart/flux/templates/deployment.yaml
• add the flag description to chart/flux/README.md
• if the flag is required but doesn't have a default, then edit all install docs