feat(community): add github-connector example app (#19961)

## Summary

Adds a new community app at
`packages/twenty-apps/community/github-connector` that demonstrates a
complete, production-style GitHub integration built on the Twenty SDK.

It is extracted (and decoupled) from the internal `twenty-eng` workspace
so external developers can use it as a reference for their own
connectors.

What it ships:

- **Six synced objects**: `pullRequest`, `pullRequestReview`,
`pullRequestReviewEvent`, `issue`, `projectItem`, `engineer`
- **Logic functions** for periodic backfills (PRs, reviews, issues,
project items, contributors) and a single signed-webhook route trigger
(`POST /github/webhook`) that performs idempotent upserts for
`pull_request`, `pull_request_review`, `issues`, and `projects_v2_item`
events
- **Views, navigation menu items and a GitHub folder** so the data is
discoverable in the UI out of the box
- **Configurable repos / project numbers** via `GITHUB_REPOS` and
`GITHUB_PROJECT_NUMBERS` application variables — no hardcoded org

## Authentication

Two interchangeable modes (PAT preferred for quick setup, GitHub App
recommended for production):

1. **Personal Access Token** — set `GITHUB_TOKEN`. Used as-is for both
REST and GraphQL.
2. **GitHub App** — set `GITHUB_APP_ID`, `GITHUB_APP_PRIVATE_KEY`,
`GITHUB_APP_INSTALLATION_ID`. Issues a signed JWT, exchanges it for a
short-lived installation token, and caches the token until expiry.

Webhook signature verification (`X-Hub-Signature-256`) is enforced when
`GITHUB_WEBHOOK_SECRET` is set.

## Notes

- Built on `twenty-sdk@2.0.0` / `twenty-client-sdk@2.0.0`
- Decoupled from internal modules (`quality/bug`, `discord`, `release`,
`code-build`, `project-management`) — `mustBeQa` is inlined and a local
`github` nav folder replaces shared ones
- `npx twenty typecheck`, `yarn lint`, and `npx twenty build` all run
cleanly
- Includes a comprehensive README with setup, env vars, webhook
configuration, and the auth resolution flow

packages/twenty-apps/community/github-connector/src/modules/shared/retry.ts

@@ -0,0 +1,49 @@
+export type RetryOptions = {
+  retries?: number;
+  baseDelayMs?: number;
+  maxDelayMs?: number;
+  shouldRetry?: (err: unknown) => boolean;
+};
+
+const sleep = (ms: number) => new Promise<void>((r) => setTimeout(r, ms));
+
+export async function retry<T>(
+  label: string,
+  fn: () => Promise<T>,
+  options: RetryOptions = {},
+): Promise<T> {
+  const requestedRetries = options.retries ?? 3;
+  const retries = Math.max(
+    Math.floor(Number.isFinite(requestedRetries) ? requestedRetries : 1),
+    1,
+  );
+  const baseDelayMs = options.baseDelayMs ?? 500;
+  const maxDelayMs = options.maxDelayMs ?? 5_000;
+  const shouldRetry = options.shouldRetry ?? (() => true);
+
+  let lastErr: unknown;
+  for (let attempt = 1; attempt <= retries; attempt++) {
+    try {
+      return await fn();
+    } catch (err) {
+      lastErr = err;
+      const msg = err instanceof Error ? err.message : String(err);
+
+      if (attempt === retries || !shouldRetry(err)) {
+        console.log(
+          `[retry] ${label} attempt ${attempt}/${retries} failed (giving up): ${msg}`,
+        );
+        throw err;
+      }
+
+      const delay = Math.min(maxDelayMs, baseDelayMs * 2 ** (attempt - 1));
+      const jittered = delay + Math.floor(Math.random() * baseDelayMs);
+      console.log(
+        `[retry] ${label} attempt ${attempt}/${retries} failed, retrying in ${jittered}ms: ${msg}`,
+      );
+      await sleep(jittered);
+    }
+  }
+
+  throw lastErr;
+}