[chore] Improve the Makefile to make it more robust to other environments.

[michaelsafyan]

Fixes

1. Failure on systems with podman-is-docker where /etc/containers/registries.conf does not contain a fallback registry for security reasons and thus requires that the container registry be specified explicitly.

2 . Failure with "fatal: No names found ..." when using make compatibility-check in developer branches.

Details

This change improves the Makefile by providing an explicit registry for the otel/weaver and otel/semconvgen containers. By default, it prefixes these with docker.io/, but uses a variable to make it easy to override.

In addition, the logic for determining the latest version of the semantic conventions is updated from using git describe to git ls-remote so that light-weight branches that haven't pulled down the list of tags can also invoke this.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
    ^^^^ Done
• schema-next.yaml updated with changes to existing conventions.
  ^^^^ N/A; does not update existing conventions