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>

e2e-tests/snapshots/github.spec.ts_disconnect-from-repo-1.aria.yml

@@ -0,0 +1,10 @@
+- button "Set up your GitHub repo":
+  - img
+- button "Create new repo"
+- button "Connect to existing repo"
+- text: Repository Name
+- textbox: "[scrubbed]"
+- paragraph: Repository name is available!
+- text: Branch
+- textbox "main"
+- button "Create Repo"