GitHub workflows (#428)

Fixes #348 
Fixes #274 
Fixes #149 

- Connect to existing repos
- Push to other branches on GitHub besides main
- Allows force push (with confirmation) dialog

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Co-authored-by: graphite-app[bot] <96075541+graphite-app[bot]@users.noreply.github.com>

src/preload.ts

@@ -46,8 +46,11 @@ const validInvokeChannels = [
   "nodejs-status",
   "install-node",
   "github:start-flow",
+  "github:list-repos",
+  "github:get-repo-branches",
   "github:is-repo-available",
   "github:create-repo",
+  "github:connect-existing-repo",
   "github:push",
   "github:disconnect",
   "get-app-version",