PHP 8.0: 32-bit and 64-bit libc builds

[joshuabenuck]

Summary

We need 32-bit and 64-bit libc builds of the PHP 8.0 agent. This ticket is part of issue #32.

Desired Behavior

• Testing is done on the platform to ensure the agent builds cleanly.
• A GitHub Actions action exists to build each on each of the libc variants.
• The actions use official PHP 8.0 docker images to perform its build.
• A GitHub Actions workflow exists that will publish artifacts suitable for inclusion in our existing jenkins builds.

Pre-reqs and dependencies

• This is one of the tickets that will block the completion of the tickets to update the jenkins jobs.
• See the MMF doc for details on the research / prototyping that was done.
• If the artifacts produced by this build are not usable on the CentOS versions used by our automated tests, we may need to fall back and build on our CentOS 5 build machines until we can migrate those tests to run on a newer OS. (Refer to the MMF doc for details on which libraries need to be updated in that case).

Additional context

See the MMF doc for more details.

[zsistla]

Please see PR #88 .