ci: fix CI after bazel 8 release

[aignas]

Summary:

• Remove the old 7.x config from all .bazelrc.
• Drop bazel 6 from example testing/support. The .bazelrc
  for enabling WORKSPACE cannot work across bazel 6,7,8.
• Add missing BUILD.bazel file for integration tests.
• Remove an integration test runner for bazel 6.x.
• RBE test for bazel 8 is still not working.
• bump rules_java for internal WORKSPACE dependencies to
  a version that supports 8.x.
• start running bazel-in-bazel integration tests using bazel 8.x.
• until fix: add sh_library loads for bazel 8.x support bazel-contrib/rules_bazel_integration_test#414 is merged,
  we need to use bazel 7 for the delete_packagese pre-commit hook,
  not sure about how to track this as the cgrindel/bazel-lib needs
  a new version.

Fixes #2378

[aignas]

Didn't have time to finish this. Tried doing:

• Bumping minimum tested version of bazel to 7.4.1
• Remove the 7.x config from bazelrc
• Add --enable_workspace to workspace only examples (actually, should we move them to internal or somewhere, so that they don't advertise WORKSPACE support anymore?).

The build is failing with rules_java and it seems that it might be defined somewhere early in the process for the WORKSPACE builds.

[aignas]

Reverted the changes and trying a more minimal stop-gap solution.

[rickeylev]

The build is failing with rules_java ...
ERROR: Error computing the main repository mapping: cannot load '@@rules_java//java:rules_java_deps.bzl': no such file

Ugh, that error. I've seen that a ton while trying to get Bazel 9 workspace working. From what I've been able to tell, it means rules_java needs to be upgraded.

Ah, I see we have CI coverage for bazel 8 bzlmod, but not workspace 🤦 .

[rickeylev]

This is what I have in some WIP stuff for bazel 9:

    http_archive(
        name = "rules_java",
        urls = [
            "https://github.com/bazelbuild/rules_java/releases/download/8.6.2/rules_java-8.6.2.tar.gz",
        ],
        sha256 = "a64ab04616e76a448c2c2d8165d836f0d2fb0906200d0b7c7376f46dd62e59cc",
    )

There may also be a change to the rules_java_dependencies() call in internal_dev_setup.bzl needed -- load("@rules_java//java:deps.bzl", "rules_java_dependencies") might be needed. (not entirely sure)