A few improvements to bcr_presubmit.py (#2077)

Stacked on
https://github.com/bazelbuild/continuous-integration/pull/2076

- Removed `MODULE_NAME` and `MODULE_VERSION` support
- Renamed `runner` to `anonymous_module_runner` to better match
[documentation](https://github.com/bazelbuild/bazel-central-registry/blob/main/docs/README.md#anonymous-module-test)
- Support overriding Bazel version in BCR task configs.
- Support specifying concurrency for jobs (default to no concurrency
limit for BCR presubmit) .