Add a new CI job to check that smithy-rs compiles on 32bit Linux-based targets (#1812)

* Replace AtomicU64 with AtomicUsize to prevent compilation issues on 32 bits platforms.

* Make sure that Rust tests compile on MacOS.

* Add CHANGELOG next entry.

* Add a new CI job to check that smithy-rs compiles on 32bit Linux-based targets.

* No trailing commas pretty please.

* Point cross at the manifest explicitly.

* Skip crates with a Python dependency. Exercise all features.

* Install required dependencies.

* Do not fail fast, we want to see the result on all platforms.

* Set paths for both commands.

* Openssl must be installed inside the cross Docker container, not on the host machine.

* Fix connector setup if `rustls` feature is not enabled.

* Restrict feature set on powerpc.

* Pass openssl env variables to the cross Docker container

* Split in two commands.

* Enable debug level logs.

* Remove openssl feature (temporarily).

* Raise verbosity.

* Trigger CI

* `native-tls`, here we go again.

* Clean up.

* Trigger CI

* Trigger CI

* Add pkg-config.

* Change include path to include arch

* Trigger CI

* Allow workflow_dispatch on ci-pr to enable triggering this CI workflow from the GitHub web interface.

* Trigger CI? Why are you doing this to me GitHub?

* Trigger CI? Are you alive GitHub?

* Fix env variables for openssl

* Use features only for rust-runtime crates.

* Check all feature combinations for aws-smithy-client

* Dry-up env variables.

* A rogue `echo` was missing

* Feature-gate doc tests based on the features they require.

* Put .github folder under shared ownership.

* Fix docs.

* Fix feature selection for doctest.

* We are using methods that are only available if rustls is enabled - adjust feature gates accordingly.

* Remove workflow dispatch trigger.