Use setup-bazel GHA

[jwnimmer-tri]

The https://github.com/bazel-contrib/setup-bazel project has matured enough where it's probably worth trying to ditch our custom yml setup and replacing it with that tool.

Besides the workflow yaml (e.g., dealing with caching) that can hopefully be removed now ...

drake-blender/.github/workflows/main.yml

Line 23 in 829a01a

# Restore the most appropriate caches.

... we also should aim to drop the related rcfile lines:

drake-blender/.github/ci.bazelrc

Lines 8 to 13 in 829a01a

	# Put the Bazel caches somewhere the CI runner will preserve them from one run
	# to the next. (All of ~/.cache/bazel_ci/ is preserved.)
	fetch --repository_cache /home/runner/.cache/bazel_ci/externals
	build --repository_cache /home/runner/.cache/bazel_ci/externals
	fetch --disk_cache /home/runner/.cache/bazel_ci/local_disk
	build --disk_cache /home/runner/.cache/bazel_ci/local_disk

[jwnimmer-tri]

The victory condition here is removing the setup code linked above, while still maintaining the invariant that for back-to-back builds (e.g., of a pull request) if the second build doesn't have any changes (e.g., rebasing the commit timestamp without any edits) then the CI turn-around time is fast (no new downloads, no tests are run, etc.).