document linux/arm64 support for official images Dec 2024 update vs sonatypecommunity

[hboutemy]

• sonatypecommunity/nexus-iq-server has been archived in December 2024, because it's not needed any more: starting with IQ Server 185, arm images are provided by official images sonatype/nexus-iq-server
• at the time of opening this issue, equivalent update has not yet been done for official sonatype/nexus3, still available only for linux/amd64: sonatypecommunity/nexus3 remains the source for linux/arm64 images for Nexus Repository

current instructions in README

cat .env-example | sed -e "s/ORGANIZATION=sonatype/ORGANIZATION=sonatype$([ $(uname -p) = "arm" ] && echo "community")/" -e "s/^UID=.*$/UID=$UID/g" -e "s/^GID=.*$/GID=$GID/g" > .env

continue to work with recent Nexus Repository, but not any more for IQ Server 185+
and nothing is done to have a different DockerHub organization for Nexus Repository different from IQ Server...

this issue is a first documentation of the change, for people using linux/arm64: we'll need to see in the future where we're going and how we should update sonatype-platform-reference

[hboutemy]

starting with Nexus 3.78, sonatype/nexus3 starts shipping arm images, like IQ Server
see release notes https://help.sonatype.com/en/sonatype-nexus-repository-3-78-0-release-notes.html#save-on-infrastructure--arm-docker-images-now-available

we should be soon able to drop the arm detection pattern