improve documentation for multi-architecture builds

[agterdenbos]

Description

Some documentation improvements for self-hosted runners on non-amd64 architectures:

1. Adds docker.io registry prefix to the qemu-user-static registration command
2. Replaces amd64 by None (host architecture)
3. Replace the multiarch/qemu-user-static image by docker.io/tonistiigi/binfmt to support container hosts other than amd64
4. Removes the reference to Multi arch builds in the Inputs for build without dockerfile section. Adds description that qemu-user-static is only needed for RUN instructions in dockerfiles.
5. Adds a note that the qemu-user-static registration remains active until the container host reboots.

Related Issue(s)

58

Checklist

• [x] This PR includes a documentation change

• [ ] This PR does not need a documentation change

• [ ] This PR includes test changes

• [ ] This PR's changes are already tested Maybe a test workflow for docker.io/tonistiigi/binfmt is desired.

• [x] This change is a patch change
• [ ] This change is a minor change
• [ ] This change is a major (breaking) change

Changes made

[tetchel]

apologies @agterdenbos, could you sign your commits? https://docs.github.com/en/github/authenticating-to-github/managing-commit-signature-verification/signing-commits

[agterdenbos]

apologies @agterdenbos, could you sign your commits? https://docs.github.com/en/github/authenticating-to-github/managing-commit-signature-verification/signing-commits

I signed them now

[divyansh42]

I've released v2.5.2 and rolled forward v2.

Thank you for this contribution! :slightly_smiling_face: