Run buildAll in prepare, move husky install to postinstall

Husky adds git hooks into the repo. We want the dev experience of

    $ git clone remote/luxon
    $ npm install # installs husky hooks
    $ ...develop develop develop...
    $ git commit
    _lint runs, everything works_

We also want to build luxon when we call npm pack or npm publish.

We also want to build luxon when it is installed somewhere else as a git
dependency
(https://docs.npmjs.com/cli/v10/configuring-npm/package-json#git-urls-as-dependencies)

Git dependencies work by running `npm install` from GitFetcher and then
depend on DirFetcher running `npm prepare` (but only prepare, not
prepack or postpack)

This change moves `husky install` to postinstall (which will,
unfortunately, still pointlessly run when we install luxon as a git
dependency). It moves the buildAll to prepare from prepack so that the
build happens when installed as a git dependency. This should preserve
existing behavior while enabling installation from git.

When installing from git and/or in CI environments, the husky command is
sometimes not available in postinstall or is available but bails out
when not run in the context of a git repo.

Author: schleyfox

package-lock.json

@@ -28,8 +28,8 @@
     "format-check": "prettier --check 'src/**/*.js' 'test/**/*.js' 'benchmarks/*.js'",
     "benchmark": "node benchmarks/index.js",
     "codecov": "codecov",
-    "prepack": "babel-node tasks/buildAll.js",
-    "prepare": "husky install",
+    "postinstall": "husky install || exit 0",
+    "prepare": "babel-node tasks/buildAll.js",
     "show-site": "http-server build"
   },
   "lint-staged": {