Make bazelisk version configurable

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")
```

Start by examining the bzlmod extension in extensions.bzl and the existing bazel_binaries configuration used with WORKSPACE. Compare how bazelisk_version is handled there with the proposed use_bazelisk call, then verify that the bzlmod form can configure the version alongside .bazelversion.

Written by the indexing model from the issue text.