automatically produce MSI files for releases

This commit:

- Adds config for building Windows installers
- Adds an action for fetching exe files built by goreleaser
- Adds an action for building Windows installers
- Adds an action for adding MSI files to an existing GH release
- Adds MSI signing to our release flow
- Disables homebrew formula bumping for prereleases
- Allows the release asset copying action to copy windows assets

.github/actions/upload-msi/index.js

@@ -0,0 +1,55 @@
+const fs = require('fs');
+const path = require('path');
+
+const github = require('@actions/github');
+const core = require('@actions/core');
+
+const GITHUB_TOKEN = process.env['GITHUB_TOKEN'];
+const MSI_PATH = 'gh.msi';
+
+process.on('unhandledRejection', function(reason, _) {
+  handleError(reason);
+});
+
+main().catch(handleError)
+
+async function main() {
+  if (!fs.existsSync(MSI_PATH)) {
+    throw new Error(`Could not find MSI file at ${MSI_PATH}`);
+  }
+  const tag = github.context.ref.replace('refs/tags/', '');
+
+  const owner = github.context.repo.owner;
+  const repo = github.context.repo.repo;
+
+
+  const release = await getRelease(GITHUB_TOKEN, owner, repo, tag);
+
+  const assetFile = fs.readFileSync(MSI_PATH);
+
+  await uploadAsset(GITHUB_TOKEN, release, assetFile);
+}
+
+async function getRelease(token, owner, repo, tag) {
+  const octokit = new github.GitHub(token);
+  const response = await octokit.repos.getReleaseByTag({ owner, repo, tag });
+  return response.data;
+}
+
+async function uploadAsset(token, release, assetFile) {
+  const octokit = new github.GitHub(token);
+  await octokit.repos.uploadReleaseAsset({
+    url: release.upload_url,
+    file: assetFile,
+    name: path.basename(MSI_PATH),
+    headers: {
+      'content-type': 'application/octet-stream',
+      'content-length': fs.statSync(MSI_PATH).size,
+    }
+  });
+}
+
+async function handleError(err) {
+  console.error(err);
+  core.setFailed(err.message);
+}