Remove condition restricting images to linux/amd64

[ikaruswill]

Fixes #3066
Flux does not process & cache multi-arch images without linux/amd64 image present.

[ikaruswill]

Based on what I saw in the code, I'm aware that flux does not know of the cluster's architecture or mixture of architectures, so when an image is cached, it is assumed to be applicable to the cluster.

Therefore the responsibility of choosing a correct repository that publishes images applicable to the cluster's architecture, is left to the user.

The default behaviour of only caching linux/amd64 perhaps helps to enforce a simple sanity check as cloud instances are mostly linux/amd64, but does not account for hybrid clusters or the increasing popularity of arm64 as evidenced by AWS Graviton2. Therefore, regardless of this sanity check, the final responsibility of repository choice and image filtering by glob/semver/regex is still, left to the user.

I'm proposing to remove this sanity check as it does not serve the purpose of abstracting the user from image compatibility concerns and may present as unexpected behaviour to some users.

[kingdonb]

Hi @ikaruswill – I saw in Flux v2 release notes that there are now ARM client binaries provided and the images are provided now using multiarch format. fluxcd/flux2#493 (comment)

This PR for Flux v1 may represent a breaking change as it changes behavior, I believe this is unlikely to be accepted as Flux v1 is formally in maintenance mode. Happy to engage the discussion further if there is any way you think the multiarch support can still be improved, but do you think this PR can be closed out?

[ikaruswill]

Sounds good @kingdonb I'm actually now waiting for Fluxv2 to reach v1 anyways. Let's close this. Thanks for taking the time to look through this anyways. Appreciate that.