Common platform builds: enhance CI to build in nested docker images

[maxgolov]

@lalitb suggested this approach during code review.

Rather than targeting 'legacy' or 'latest' compiler and a default set of GitHub action images, we can implement better (and faster) test coverage with the following CI loop in nested Docker images:

OS	Compiler
Ubuntu 14.04	gcc-4.8
Ubuntu 16.04	gcc-5.3.1
Ubuntu 18.04	gcc-7.4.0
Ubuntu 20.04	gcc-9.x.x (and gcc-10.x.x)

Draft PR that adds these containers. But does not yet add these to the CI yet is here: #377

Above configurations are tested and known to work, passing all core tests. We can also add RHEL and CentOS images (yum / rpm-based distros) as well. The aim is to iteratively build and run these Docker images on a GitHub Actions Linux runner, using GitHub cache (up to 5GB per repo) - to save the cached images. This GitHub action seems to be implementing what's needed:
https://github.com/marketplace/actions/build-docker-images-using-cache

Linux docker allows for nested containers: running docker container in GitHub action (which itself is run in docker container).

We can organize a build farm for up to 10 popular Linux repos using one set of build tools: tools/build.sh

Anyone can later reuse this effort to build OpenTelemetry C++ SDK PPA for Ubuntu or alike. Personal Package Archives (PPA) allow you to upload Ubuntu source packages to be built and published as an apt repository by Launchpad.

[maxgolov]

Partially addressed by #377 ... I'll use this issue to describe the process in a markdown document, plus try it out on Linux image GitHub Action runner. Basically Ubuntu 20.04 GitHub Actions image may itself kick-off docker'ized build of all other Linux builds.

[github-actions]

This issue was marked as stale due to lack of activity. It will be closed in 7 days if no furthur activity occurs.

[github-actions]

This issue was marked as stale due to lack of activity. It will be closed in 7 days if no furthur activity occurs.

[lalitb]

tagging @esigo just for information, as he is doing some work on creating multiplatform docker images.