allow other directors that tools/ for the wrapper

[holgerschurig]

Hi, can we have BAZELISK_WRAPPER_DIR variable where we can e.g. bin as the directory of the wrapper? Or, alternatively, a BAZELISK_WRAPPER= that points directly to the wrapper. We'd then loose then the various extensions it supports ... but if someone configures the wrapper in the .bazeliskrc file, then this might not be a problem.

The reason is that the current tools/ constant forces a policy into all usages. I.e. any repository that wants to use this bazel feature needs a top-level "tools/" directory which might not be prudent for the project. Or for the projects leaders opinion ...

[keith]

https://github.com/bazelbuild/bazelisk/pull/567