Migrate to SLE BCI images

[thomasferrandiz]

This PR removes the usage of alpine images and replaces them with SLE BCI images.

[pgonin]

poke @macedogm

[pgonin]

build fail because of no matching manifest for linux/arm/v7 in the manifest list entries
I don't think we need to keep building for arm v7

[macedogm]

@pgonin I spoke with Caleb about armv7 and we don't need to build for this arch, so it's safe to remove it from the build pipeline. I had do to it also for some of the PRs that I opened. We need to build and ship only amd64, s390x and arm64.

[macedogm]

We just need to remove the build step for armv7 from Drone, then LGTM.

[macedogm]

LGTM

[dweomer]

Why SLES here instead of BCI? Unpacked on my system, the SLES image is 7 times larger than Alpine.

[thomasferrandiz]

In fact it looks like bci-base and sle15 images are identical.
If you check here, they have the same digest:
https://registry.suse.com/static/suse/sle15sp3/index.html
https://registry.suse.com/static/bci/bci-base/index.html

But I agree it is unfortunate that they are so large.

There are also bci-minimal and bci-micro images which are small but they are still in Tech Preview.
As I understand, @macedogm is preparing a proposal to use them with sidecars but I don't know if we can use that yet.

[macedogm]

I'm discussing internally about which image to "standardize". I don't believe that we will follow with the idea of the sidecar, but actually with a mix of bci-micro and bci-base/sle15 (when really needed). Let's see how it'll progress.

[cbron]

registry.suse.com/suse/sle15:15.3 is sle-bci, not full SLES.

[dweomer]

This is also a go version bump. In trying to see if the go.mod/go.sum would change with a go mod tidy I ran into:

$ go mod tidy
go: downloading github.com/docker/distribution v2.8.0+incompatible
verifying github.com/docker/distribution@v2.8.0+incompatible: checksum mismatch
        downloaded: h1:u9vuu6qqG7nN9a735Noed0ahoUm30iipVRlhgh72N0M=
        go.sum:     h1:l9EaZDICImO1ngI+uTifW+ZYvvz7fKISBAKpg+MbWbY=

SECURITY ERROR
This download does NOT match an earlier download recorded in go.sum.
The bits may have been replaced on the origin server, or an attacker may
have intercepted the download attempt.

For more information, see 'go help module-auth'.

Fixed via #196