Add --immutable arg

[chrisdothtml]

Adds a new --immutable arg to the install command so that it has parity with how yarn behaves with --immutable with regard to generated files.

Currently, in "immutable" cases (i.e. when running jz ci), jazelle skips the file generation altogether (.bazelignore and BUILD.bazel files).

This PR changes it so that when --immutable is passed (either explicitly via jz install --immutable or implicitly via jz ci), it will run the file generation, but fail if any files need to be created/changed. In the failure case it emits an error message listing the files that would have changed.

This is what it looks like to a user when it fails:

[chrisdothtml]

There was a bug in this util that was generating a dangling comma in the deps list for BUILD.bazel files which looked like this:

web_library(
    name = "library",
    deps = [,
        
    ],
    srcs = glob(["**"], exclude = ["dist/**"]),
)

This was necessary to fix the testBatchTestGroup test (its behavior changed after my update because it internally calls an immutable install, which was failing due to changed generated files)