[bzlmod] first pin operation produces file with wrong name

[alexeagle]

Related to the lack of documentation for using this repo with bzlmod, I'm trying to write this up and running into some issues:

With this repro:

MODULE.bazel

bazel_dep(name = "rules_jvm_external", version = "4.5")
maven = use_extension("@rules_jvm_external//:extensions.bzl", "maven")

maven.install(
    artifacts = ["org.seleniumhq.selenium:selenium-java:4.4.0"],
)

use_repo(maven, "maven")

then bazel run @maven//:pin and it creates a file named rules_jvm_external~4.5~maven~maven_install.json

I think this was meant to be just maven_install.json

[vorburger]

Update https://github.com/bazelbuild/rules_jvm_external/blob/master/docs/bzlmod.md#installation when done.