Avoid downloading musl-x86_64 on every build

In order to support musl linux on x86_64 for our native features (e.g. universal profiling integration), we have been downloading a pre-built musl compiler chain from https://musl.cc/. The owners of that site have been bombed with lots of requests from GH-actions, to which we might have contributed too. Therefore they decided to block Microsoft hosts, which causes our builds to fail.

https://github.com/elastic/elastic-otel-java/pull/661 implements a band-aid fix by simply hosting the binary for now in a different GH repo, as I did not want to bloat the size of this repo by checking in a 110mb binary.

We should probably look into having a separate repo to generate our cross-compilation docker images and have them easily accessible in gh-packages. This would greatly speed up our builds too, as currently most of the time is spent generating those images.