[Idea]: Bootstrap bazelisk

[arrdem]

Today the ctx.bazel machinery expects that the user has a bazel on their $PATH somewhere. Ideally the Aspect CLI would do the right thing and mostly stand alone, which means provisioning a bazelisk transparently by default.

• Add a new cache.axl implementation transliterating the current cache crate
• Add a new bazelisk.axl implementation which consumes the current HTTP feature(s) and the cache package to provide a helper for downloading a bazelisk binary
• Extend the reference config.axl to use the bazelisk.axl and install a bazel binary into the config struct.
• Extend the ctx.bazel machinery to go through the config struct to get the path of the bazel nominal binary.