[release/1.6 backport] rpm: minimal RHEL support

[thaJeztah]

backport of:

• [main] RHEL PoC #342 for the release/1.6 branch
• [main] Makefile: add registry.access.redhat.com to known registries #380
• [main] rpm: minimal RHEL support (carry #342) #381

[thaJeztah]

Wait; why is this failing on btrfs?

#27 20.24 + man/containerd.8
#27 20.24 go run -mod=readonly  cmd/gen-manpages/main.go containerd.8 man
#27 21.23 + man/containerd-config.8
#27 21.23 go-md2man -in "docs/man/containerd-config.8.md" -out "man/containerd-config.8"
#27 21.23 + man/containerd-config.toml.5
#27 21.23 go-md2man -in "docs/man/containerd-config.toml.5.md" -out "man/containerd-config.toml.5"
#27 21.24 WARNING: go-md2man does not handle node type HTMLBlock
#27 21.24 + man
#27 21.24 + BUILDTAGS=
#27 21.24 + GO111MODULE=auto
#27 21.24 + make -C /go/src/github.com/containerd/containerd VERSION=0.20240725.000514~d157b85 REVISION=d157b8583cf797c42c13c20845c4608a889ae2e1 PACKAGE=containerd.io BUILDTAGS=
#27 21.24 make: Entering directory '/go/src/github.com/containerd/containerd'
#27 21.30 + bin/ctr
#27 36.12 + bin/containerd
#27 41.20 # github.com/containerd/btrfs
#27 41.20 vendor/github.com/containerd/btrfs/btrfs.go:21:10: fatal error: btrfs/ioctl.h: No such file or directory
#27 41.20    21 | #include <btrfs/ioctl.h>
#27 41.20       |          ^~~~~~~~~~~~~~~
#27 41.20 compilation terminated.
#27 47.83 make: *** [Makefile:254: bin/containerd] Error 1
#27 47.83 make: Leaving directory '/go/src/github.com/containerd/containerd'
#27 47.83 error: Bad exit status from /var/tmp/rpm-tmp.p74w7K (%build)
#27 47.83     line 40: It's not recommended to have unversioned Obsoletes: Obsoletes: containerd
#27 47.83     line 41: It's not recommended to have unversioned Obsoletes: Obsoletes: runc
#27 47.83     Bad exit status from /var/tmp/rpm-tmp.p74w7K (%build)
#27 47.83 
#27 47.83 RPM build warnings:
#27 47.83 
#27 47.83 RPM build errors:
#27 ERROR: process "/bin/sh -c /root/build-rpm" did not complete successfully: exit code: 1

[thaJeztah]

closing, as we moved our release pipeline to use https://github.com/docker/packaging;

• README: Deprecate this repo #429