Installation: add extra components for image automation

[valentin-krasontovitsch]

regarding bootstrapping - i'm coming from the docs on gitlab, trying to setup an integration for "gitops" between gitlab and flux.

i followed the install bootstrapping guide, and it was good.

i deployed something with flux, and again it was good.

i finally got to the point where i want manual image updates, looked at the guide, and failed (after creating an image repo and an imagepolicy) with the message no matches for kind "Image Policy" in version "image.toolkit.fluxcd.io/v1beta2"

i was confused - maybe old docs, maybe this api has matured beyond beta2, but no, i found the imagepolicy to live in exactly that api.

after some more gooling i found out (in the migrate to flux v2 guide) that flux needs to be configured with some extra components for image automation.

I propose adding a hint about the extra components needed for image automation, or straight out just including them in the example bootstrapping invocations.

i suppose, based on the name extra components, and the fact that they are left out, that perhaps not every flux user has the same use case as me, namely using flux for image automation, so maybe you had some very good reasons for writing it the way you did. perhaps just hinting at the possible necessity of running with the extra components might be enough...