Make bazelisk version configurable

[katre]

As part of #181, Bazelisk will be used to download the Bazel used for tests.

With the legacy WORKSPACE support, the Bazelisk version can be configured in the bazel_binaries call:

bazel_binaries(
    bazelisk_version = "1.17.0",
    versions = [
        "//:.bazelversion",
    ],
)

This is not currently possible with the bzlmod support, and should be added.

Possible syntax (this does not work currently):

bazel_binaries = use_extension(
    "@rules_bazel_integration_test//:extensions.bzl",
    "bazel_binaries",
    dev_dependency = True,
)
bazel_binaries.download(version_file = "//:.bazelversion")
bazel_binaries.use_bazelisk("1.17.0")
use_repo(bazel_binaries, "bazel_binaries")

[katre]

It would also be handy to have a way to use a local (non-hermetic) bazelisk, to help uncommon os/arch setups.